研究者総覧

渕崎 員弘 (フチザキ カズヒロ)

  • 大学院理工学研究科 数理物質科学専攻 教授
Last Updated :2020/11/10

研究者情報

学位

  • 工学博士(大阪大学)
  • 工学修士(京都大学)

ORCID ID

J-Global ID

研究キーワード

  • 位相欠陥   ガラス転移   非平衡統計力学   ポリアモルフィズム   

研究分野

  • 自然科学一般 / 数理物理、物性基礎

経歴

  • 2017年04月 - 2018年03月  東京大学物性研究所客員教授
  • 2005年04月 - 2006年03月  分子科学研究所分子基礎理論第四研究部門客員教授
  • 2003年 - 2006年  愛媛大学理学部Faculty of Science教授
  • 2006年  - 愛媛大学理工学研究科教授
  • 2000年 - 2003年  愛媛大学理学部Faculty of Science助教授
  • 1999年 - 2000年  九州大学大学院理学研究科
  • 1991年 - 1999年  九州大学理学部School of Sciences
  • 1990年 - 1991年  日本原子力研究所
  • 1989年 - 1990年  日本原子力研究所

学歴

  •         - 1989年   大阪大学   Graduate School, Division of Engineering Science
  •         - 1983年   京都大学   Faculty of Engineering

所属学協会

  • American Chemical Society   American Association for the Advancement of Science   日本高圧力学会   日本物理学会   American Association for the Advancement of Science   American Association for the Advancements of Science   

研究活動情報

論文

  • Hiroki Naruta, Kazuhiro Fuchizaki, Daisuke Wakabayashi, Akio Suzuki, Ayako Ohmura, Hiroyuki Saitoh
    Journal of Physics Condensed Matter 32 5 2020年 [査読有り]
     研究論文(学術雑誌) 
    © 2019 IOP Publishing Ltd. A SnI4 molecule lowers its symmetry from T d to C3v on the liquid-liquid transition. Because it is possible to lower the molecular symmetry without violating the crystalline symmetry, it is worth examining whether the deformation occurs in the crystalline phase field. Extended X-ray absorption fine structure (EXAFS) measurements on the crystalline state were carried out to investigate the change in the environment around a Sn atom at high pressures and temperatures. We could not find clear evidence on the symmetry change of molecules even close to the melting points, where the melting curve becomes abnormally flat against pressure. Indeed, no inconsistency was found when we assumed that the coordination number of a Sn atom remains unchanged in the temperature and pressure range examined. The situation remains true when the system entered the high-pressure crystalline phase on compression. We can propose a consistent scenario as to the structural change on the phase transformation. The incompressibility of a SnI4 molecule could be suitably quantified. The procedure enabled us to conclude the molecule is more than an order of magnitude incompressible than the lattice.
  • Chikara Shito, Keitaro Okamoto, Yuki Sato, Ryuji Watanabe, Tomonori Ohashi, Kazuhiro Fuchizaki, Takahiro Kuribayashi, Akio Suzuki
    HIGH PRESSURE RESEARCH 39 3 499 - 508 2019年07月 [査読有り]
     研究論文(学術雑誌) 
    High pressure hydrous phases with distorted rutile-type structure have attracted much interest as potential water reservoirs in the Earth's mantle. An in-situ X-ray diffraction study of beta-CrOOH was performed at high pressures of up to 6.2 GPa and high-temperatures of up to 700 K in order to clarify the temperature effect on compression behaviors of beta-CrOOH. The P-V-T data fitted to a Birch-Murnaghan equation of state yielded the following results: isothermal bulk modulus K-T0 = 191(4) GPa, temperature derivative ( partial differential K-T/ partial differential T)(P) = -0.04(2) GPa K-1, and volumetric thermal expansion coefficient alpha = 3.3(2) x 10(-5) K-1. In this study, at 300 K, the a-axis became less compressible at pressures above 1-2 GPa. We found that the pressure where the slopes of a/b and a/c ratios turned positive increased with temperature. This is the first experimental study indicating the temperature dependence of the change in the axial compressibility in distorted rutile-type M3+OOH.
  • Fuchizaki Kazuhiro
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 88 6 2019年06月 [査読有り]
  • Fuchizaki Kazuhiro, Naruta Hiroki, Sakagami Takahiro
    JOURNAL OF PHYSICS-CONDENSED MATTER 31 22 2019年06月 [査読有り]
  • Fuchizaki Kazuhiro, Sakagami Takahiro, Iwayama Hiroshi
    JOURNAL OF CHEMICAL PHYSICS 150 11 2019年03月 [査読有り]
  • Fuchizaki Kazuhiro, Watanabe Kei
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 11 2018年11月 [査読有り]
  • Kazuma Okamoto, Kazuhiro Fuchizaki
    Molecular Simulation 44 5 384 - 388 2018年03月 [査読有り]
     研究論文(学術雑誌) 
    A new ‘two-phase’ simulation method with which to accurately predict the melting curve is proposed. The method requires, as a starting configuration, generating a two-phase coexistence state by employing a suitable ensemble. Examining a change in volume ratio of the two phases upon varying temperature (pressure) under a fixed pressure (temperature) allows us to determine the phase transition point. The Clausius–Clapeyron relationship can then be implemented as a guide to predict the nearby phase transition point. The method was applied to determine the solid–liquid phase boundary of the modified Lennard–Jones system. A better accuracy, as that achieved by the non-equilibrium relaxation method (Asano Y, Fuchizaki K. J Phys Soc Jpn. 2017 86:025001), was obtained but with much less computational cost.
  • Kazuhiro Fuchizaki, Hironori Nishimura, Takaki Hase, Hiroyuki Saitoh
    Journal of Physics Condensed Matter 30 4 2018年01月 [査読有り]
     研究論文(学術雑誌) 
    The similarity in the shape of the melting curve of GeI4 to that of SnI4 suggests that a liquid-liquid transition as observed in liquid SnI4 is also expected to occur in liquid GeI4. Because the slope of the melting curve of GeI4 abruptly changes at around 3 GPa, in situ synchrotron diffraction measurements were conducted to examine closely the structural changes upon compression at around 3 GPa. The reduced radial distribution functions of the high- and low-pressure liquid states of GeI4 share the same feature inherent in the high-pressure (high-density) and low-pressure (low-density) radial distribution functions of liquid SnI4. This feature allows us to introduce local order parameters that we may use to observe the transition. Unlike the transition in liquid SnI4, the transition from the low-pressure to the high-pressure structure seems sluggish. We speculate that the liquid-liquid critical point of GeI4 is no longer a thermodynamically stable state and is slightly located below the melting curve. As a result, the structural change is said to be a crossover rather than a transition. The behavior of the local-order parameters implies a metastable extension of the liquid-liquid phase boundary with a negative slope.
  • 市東 力, 岡本 啓太郎, 佐藤 勇輝, 渡邉 隆二, 大橋 智典, 渕崎 員弘, 栗林 貴弘, 鈴木 昭夫
    日本鉱物科学会年会講演要旨集 2018 0 84 - 84 一般社団法人日本鉱物科学会 2018年 [査読有り]
     
    δ-AlOOHに代表される変形ルチル型M3+OOHの構造は,M3+O6八面体とO-H...O水素結合からなる.変形ルチル型M3+OOHの特徴的な圧縮特性変化として,体積弾性率の増加とa/cb/c軸率の変化を伴うstiffeningという現象が観測されている(Sano-Furukawa et al. 2012, Kuribayashi et al. 2014).本研究では,変形ルチル型構造をもつguyanaite (β-CrOOH)について温度圧力特性を調べ,P-V-T状態方程式の決定を試みた.5 GPa,900 Kでguyanaiteを合成し,エネルギー分散型粉末X線回折実験を温度300-700 K,圧力0-6 GPaの範囲で行った.結果からKT0 = 191±20 GPa,α = (3.3±1.5)×10-5 K-1 という値を得た.常温での測定では,a, b軸がc軸よりも圧縮しにくいということが確かめられ,Sano-Furukawa et al. (2012)と定性的に一致する.
  • Kazuma Okamoto, Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 6 2017年06月 [査読有り]
     研究論文(学術雑誌) 
    The melting curve of MgO, an important compound dissociated from the component of the Earth's lower mantle, was predicted in this work by using a one-phase approach. The existing data for the melting points under pressures were used as input. The necessary thermodynamic information was supplemented by constructing the equation of state. The melting point near the core-mantle boundary was estimated to be approximately 6000 K.
  • Ayano Chiba, Masanori Inui, Yukio Kajihara, Kazuhiro Fuchizaki, Ryo Akiyama
    The Journal of Chemical Physics 146 19 194503-1 - 194503-5 American Institute of Physics 2017年05月 [査読有り]
     研究論文(学術雑誌)
  • Ayano Chiba, Masanori Inui, Yukio Kajihara, Kazuhiro Fuchizaki, Ryo Akiyama
    JOURNAL OF CHEMICAL PHYSICS 146 19 2017年05月 [査読有り]
     研究論文(学術雑誌) 
    A pressure-induced structural change of a polymer isotactic poly(4-methyl-1-pentene) (P4MP1) in the melted state at 270 degrees C has been investigated by high-pressure in situ x-ray diffraction, where high pressures up to 1.8 kbar were applied using helium gas. The first sharp diffraction peak (FSDP) position of the melt shows a less pressure dependence than that of the normal compression using a solid pressure transmitting medium. The contraction using helium gas was about 10% at 2 kbar, smaller than about 20% at the same pressure using a solid medium. The result indicates that helium entered the interstitial space between the main chains. The helium/monomer molar ratio was estimated to be 0.3 at 2 kbar from the FSDP positions. These results suggest that the compressibility of the P4MP1 melt can be largely dependent on the pressure transmitting media. As the pore size is reversibly and continuously controllable by compression, we suggest that the P4MP1 melt can be an ideal porous liquid for investigating a novel mechanical response of the pores in a non-crystalline substance. Published by AIP Publishing.
  • Takahiro Sakagami, Kazuhiro Fuchizaki
    JOURNAL OF PHYSICS-CONDENSED MATTER 29 14 2017年04月 [査読有り]
     研究論文(学術雑誌) 
    The existence of a network structure consisting of electrically neutral tetrahedral molecules in liquid SnI4 and GeI4 at ambient pressure was examined. The liquid structures employed for the examination were obtained from a reverse Monte Carlo analysis. The structures were physically interpreted by introducing an appropriate intermolecular interaction. A 'bond' was then defined as an intermolecular connection that minimizes the energy of intermolecular interaction. However, their 'bond' energy is too weak for the 'bond' and the resulting network structure to be defined statically. The vertex-to-edge orientation between the nearest molecules is so ubiquitous that almost all of the molecules in the system can take part in the network, which is reflected in the appearance of a prepeak in the structure factor.
  • Kazuma Okamoto, Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 3 2017年03月 [査読有り]
     研究論文(学術雑誌) 
    The critical parameters of the modified Lennard-Jones system were examined. The isothermal-isochoric ensemble was generated by conducting a molecular dynamics simulation for the system consisting of 6912, 8788, 10976, and 13500 particles. The equilibrium between the liquid and vapor phases was judged from the chemical potential of both phases upon establishing the coexistence envelope, from which the critical temperature and density were obtained invoking the renormalization group theory. The finite-size scaling enabled us to finally determine the critical temperature, pressure, and density as T-c = 1.0762(2), p(c) = 0.09394(17), and rho(c) = 0.331(3), respectively.
  • Yuta Asano, Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 2 2017年02月 [査読有り]
     研究論文(学術雑誌) 
    The melting curve of the modified Lennard-Jones system, which has been obtained by equating the free energies between the solid and liquid phases, was reinvestigated using the nonequilibrium relaxation method. The latter method satisfactorily reproduced the previous result with much simplified procedures.
  • Kazuhiro Fuchizaki, Takahiro Sakagami, Shinji Kohara, Akitoshi Mizuno, Yuta Asano, Nozomu Hamaya
    JOURNAL OF PHYSICS-CONDENSED MATTER 28 44 2016年11月 [査読有り]
     研究論文(学術雑誌) 
    A molecular liquid GeI4 is a candidate that undergoes a pressure-induced liquid-to-liquid phase transition. This study establishes the reference structure of the low-pressure liquid phase. Synchrotron x-ray diffraction measurements were carried out at several temperatures between the melting and the boiling points under ambient pressure. The molecule has regular tetrahedral symmetry, and the intramolecular Ge-I length of 2.51 angstrom is almost temperatureindependent within the measured range. A reverse Monte Carlo (RMC) analysis is employed to find that the distribution of molecular centers remains self-similar against heating, and thus justifying the length-scaling method adopted in determining the density. The RMC analysis also reveals that the vertex-to-face orientation of the nearest molecules are not straightly aligned, but are inclined at about 20 degrees, thereby making the closest intermolecular I-I distance definitely shorter than the intramolecular one. The prepeak observed at similar to 1 angstrom(-1) in the structural factor slightly shifts and increases in height with increasing temperature. The origin of the prepeak is clearly identified to be traces of the 111 diffraction peak in the crystalline state. The prepeak, assuming the residual spatial correlation between germanium sites in the densest direction, thus shifts toward lower wavenumbers with thermal expansion. The aspect that a relative reduction in molecular size associated with the volume expansion is responsible for the increase in the prepeak's height is confirmed by a simulation, in which the molecular size is changed.
  • T. Sakagami, K. Fuchizaki, K. Ohara
    JOURNAL OF PHYSICS-CONDENSED MATTER 28 39 2016年10月 [査読有り]
     研究論文(学術雑誌) 
    We propose a novel approach with which to estimate the density of liquids. The approach is based on the assumption that the systems would be structurally similar when viewed at around the length scale (inverse wavenumber) of the first peak of the structure factor, unless their thermodynamic states differ significantly. The assumption was implemented via a similarity transformation to the radial distribution function to extract the density from the structure factor of a reference state with a known density. The method was first tested using two model liquids, and could predict the densities within an error of several percent unless the state in question differed significantly from the reference state. The method was then applied to related real liquids, and satisfactory results were obtained for predicted densities. The possibility of applying the method to amorphous materials is discussed.
  • 渕崎 員弘, 大村 彩子, 鈴木 昭夫, 西田 圭佑, 浜谷 望, 齋藤 寛之
    日本物理学会講演概要集 71 0 3030 - 3030 一般社団法人 日本物理学会 2016年 [査読有り]
     

    ヨウ化錫液体に対して圧力下での放射光X線その場吸収測定を行った。1 GPa未満、1200 K〜1400 Kの領域で吸収の極大を観測した。これは、この領域で流体密度が極大となっていることを示すものである。SPring-8だけでなくKEKでの実験によって再現性を確認した。これははほぼ平均場計算の予想(渕崎ら, 日本物理学会第65回年次大会,22pHY–5)通りである。

  • 渕崎 員弘, 大村 彩子, 鈴木 昭夫, 西田 圭佑, 浜谷 望, 齋藤 寛之
    日本物理学会講演概要集 71 0 2962 - 2962 一般社団法人 日本物理学会 2016年 [査読有り]
     

    ヨウ化錫液体に対して圧力下での放射光X線その場吸収測定を行った。950 K〜1000 Kに保ったまま、圧力印加したところ、吸収の急激な増加を1.5 GPa付近で検出した。一方、1200 Kでの圧力印加ではなだらかな吸収増加を観測するのみであった。これは臨界点が1.5 GPa付近、1000 K〜1200 Kの間に存在することを示すものである。SPring-8だけでなくKEKでの実験によって再現性を確認した。第二臨界点の位置はほぼ平均場計算の予想(K. Fuchizaki et al., JCP 135, 091101 (2011))通りである。

  • Kazuhiro Fuchizaki, Kazuma Okamoto
    PHYSICS LETTERS A 380 1-2 293 - 298 2016年01月 [査読有り]
     研究論文(学術雑誌) 
    The melting curve of the modified Lennard-Jones solid is derived using a one-phase approach. The Pade approximation employed for solving the melting-curve equation converges at the middle stage, giving rise to the well-known Simon curve that satisfactorily captures the actual melting curve found from a molecular dynamics simulation over a pressure range of four orders of magnitude. This situation is justified because the solid under consideration was shown to satisfy the thermodynamic condition under which Simon's curve becomes exact. (C) 2015 Elsevier B.V. All rights reserved.
  • Kazuhiro Fuchizaki, Kazuma Okamoto, Seishiro Doi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 8 2015年08月 [査読有り]
     研究論文(学術雑誌) 
    An equation of state (EOS) was constructed for the modified Lennard-Jones (mLJ) solid. States not close to the melting point are accurately described by the EOS. A "pretransitional" behavior was detected for the temperature derivative of the bulk modulus near the temperature at which the melting curve bends appreciably.
  • Kazuhiro Fuchizaki, Yuta Asano
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 6 2015年06月 [査読有り]
     研究論文(学術雑誌) 
    A model molecular crystalline GeI4 was examined using molecular dynamics simulation. The model was constructed in such a way that rigid tetrahedral molecules interact with each other via Lennard-Jones potentials whose centers are located at the vertices of a tetrahedron. Because no other interaction that can "soften" the intermolecular interaction was introduced, the melting curve of the model crystalline material does not exhibit the anomaly that was found for the real substance. However, the current investigation is useful in that it could settle the upper bound of pressure below which the model can predict properties of the molecular liquid. Moreover, singularity-free nature of the melting curve allowed us to analytically treat the melting curve in the light of the Kumari-Dass-Kechin equation. As a result, we could definitely conclude that the well-known Simon equation for the melting curve is merely an approximate expression. The condition for the validity of Simon's equation was identified.
  • Kazuhiro Fuchizaki, Nozomu Hamaya
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 83 7 2014年07月 [査読有り]
     研究論文(学術雑誌) 
    In situ synchrotron x-ray diffraction measurements were carried out to determine the melting curve of the molecular crystal GeI4. We found that the melting line rapidly increases with a pressure up to about 3 GPa, at which it abruptly breaks. Such a strong nonlinear shape of the melting curve can be approximately captured by the Kumari-Dass-Kechin equation. The parameters involved in the equation could be determined from the equation of state for the crystalline phase, which was also established in the present study. The melting curve predicted from the equation approaches the actual melting curve as the degree of approximation involved in obtaining the equation is improved. However, the treatment is justifiable only if the slope of the melting curve is everywhere continuous. We believe that this is not the case for GeI4's melting line at the breakpoint, as inferred from the nature of breakdown of the Kraut-Kennedy and the Magalinskii-Zubov relationships. The breakpoint may then be a triple point among the crystalline phase and two possible liquid phases.
  • Yuta Asano, Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 83 3 2014年03月 [査読有り]
     研究論文(学術雑誌) 
    We have proposed a modified Lennard-Jones (mLJ) potential to deal with problems, such as the accurate determination of the melting condition, in which an attractive interaction plays an essential role, but its range need not necessarily extend to infinity. An accurate phase diagram, including the triple and the critical points of the system characterized by the mLJ potential, has been investigated using mainly thermodynamic integration. To predict the thermodynamic behavior of the system, it is further desired to construct the equation of state (EOS) as accurately as possible. The modified Benedict-Webb-Rubin EOS was employed to this end. The 33 parameters involved in the equation were carefully determined in order for the EOS to be compatible with the temperature dependences of the virial coefficients as well as with an extremely large set of thermodynamic data obtained from our own molecular dynamics simulation performed over a wide fluid region. The resultant EOS was found to be not only sufficiently accurate at temperatures up to twenty times as high as the critical-point temperature but also effective in practical use.
  • Kazuhiro Fuchizak, Yuta Asano
    Journal of the Physical Society of Japan 82 12 2013年12月 [査読有り]
     研究論文(学術雑誌) 
    The Lennard-Jones (LJ) potential has been widely used, even beyond fluid science, as a standard form to express interparticle interaction. However, numerical computation and simulation requires some convention for dealing with the potential's infinite tail. This delicate problem can be circumvented by adopting a truncated potential. The functional form of the latter should mimic that of the original potential as closely as possible, while simultaneously minimizing artificial effects caused by the resultant discontinuities. The advantage of choosing such a truncated LJ potential, called the modified Lennard-Jones (mLJ) potential, is that the thermodynamic behavior of fluids can be predicted from the extensive knowledge base regarding the LJ fluid. In this study, the properties of the mLJ fluid were treated as perturbations of the LJ fluid case, and the discrepancies were expressed as density series expansions. The second virial coefficient of the mLJ fluid was well reproduced by this method. Reproduction of the liquid-vapor coexisting envelope was also satisfactory, except in the vicinity of the critical point. © 2013 The Physical Society of Japan.
  • Kazuhiro Fuchizaki
    JOURNAL OF CHEMICAL PHYSICS 139 24 2013年12月 [査読有り]
     研究論文(学術雑誌) 
    The low-pressure crystalline phase of a molecular crystal, SnI4, has a rising melting curve that breaks abruptly at around 1.5 GPa, beyond which it becomes almost flat, with a slight maximum at about 3 GPa. Although the overall aspect of this melting curve can be captured by the Kumari-Dass-Kechin equation, the values for the parameters involved in the equation were definitely different from those predicted on the basis of the Clapeyron-Clausius relationship. On the other hand, the accuracy of our experimental data prevented us from judging whether the parameters are derivable from the Lindemann melting law, as shown independently by Kumari and Dass, and by Kechin. The Kraut-Kennedy and Magalinskii-Zubov relationships seem to be valid in the low-pressure region where the melting curve is rising. The breakdown of these relationships suggests a qualitative change in the intermolecular interaction upon compression, thereby making the melting behavior unusual. (C) 2013 AIP Publishing LLC.
  • Kazuhiro Fuchizaki, Yuta Asano
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 3 2013年03月 [査読有り]
     研究論文(学術雑誌) 
    By adopting the isothermal-isochoric ensemble instead of the isothermal-isobaric one, the density of the modified Lennard-Jones system could be specified unambiguously even under extremely low-pressure conditions. The Gibbs free energy of the gaseous state could thereby be calculated with sufficient accuracy. For practical applications of the free energy, the lowest correction in the virial expansion was found to be sufficient under pressure conditions below 0.001 epsilon/sigma(3), where epsilon and sigma are the energy and length parameters, respectively, of the modified Lennard-Jones potential. Comparison of this free energy with those for the condensed phases obtained hitherto gave well-defined sublimation points. These points then defined the equilibrium solid-gas phase boundary. The present study thus confirmed the location of not only a sublimation point found previously under marginally stable conditions of an isobaric ensemble, but also the triple point; its temperature and pressure were speculated to be 0.61 epsilon/k(B) and 0.0018 +/- 0.0005 epsilon/sigma(3), respectively, where k(B) denotes Boltzmann's constant.
  • Kazuhiro Fuchizaki, Nozomu Hamaya, Yoshinori Katayama
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 3 2013年03月 [査読有り]
     研究論文(学術雑誌) 
    An in situ synchrotron x-ray absorption measurement was carried out to estimate the density of liquid SnI4. The characteristic densities of the low-and high-pressure liquids were found to be 4.6-4.7 and 4.9-5.0 g/cm(3), respectively, and their region is separated at around 1.7 GPa. The difference in density, although a slight amount of 0.3-0.4 g/cm(3), strongly suggests the existence of a weak but discontinuous phase transition at that pressure between the two liquid regions.
  • Yuta Asano, Kazuhiro Fuchizaki
    JOURNAL OF CHEMICAL PHYSICS 137 17 2012年11月 [査読有り]
     研究論文(学術雑誌) 
    An investigation of the precise determination of melting temperature in the modified Lennard-Jones system under pressure-free conditions [Y. Asano and K. Fuchizaki, J. Phys. Soc. Jpn. 78, 055002 (2009)] was extended under finite-pressure conditions to obtain the phase diagram. The temperature and pressure of the triple point were estimated to be 0.61 epsilon/k(B) and 0.0018(5) epsilon/sigma(3), and those of the critical point were 1.0709(19) epsilon/k(B) and 0.1228(20) epsilon/sigma(3), where epsilon and sigma are the Lennard-Jones parameters for energy and length scales, respectively, and k(B) is the Boltzmann constant. The potential used here has a finite attractive tail and does not suffer from cutoff problems. The potential can thus be a useful standard in examining statistical-mechanical problems in which different treatments for the tail would lead to different conclusions. The present phase diagram will then be a useful guide not only for equilibrium calculations but also for nonequilibrium problems such as discussions of the limits of phase (in)stability. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764855]
  • Kazuhiro Fuchizaki, Nozomu Hamaya
    Physical Review B - Condensed Matter and Materials Physics 84 14 2011年10月 [査読有り]
     研究論文(学術雑誌) 
    The molecular crystal of tin tetraiodide is known to exhibit unusual features under pressure, such as solid-state amorphization. The low-pressure crystalline phase has a melting curve with a maximum at about 1.5 GPa, dividing the liquid phase into two states with different structures. However, the thermodynamic properties of this solid phase are still unknown. For proper thermodynamic measurements for the solid phase, we present here the Parsafar-Mason and Birch-Murnaghan-Anderson equations of state for the phase as a predecessor. The validity of the equations was confirmed by recent experimental observations. As far as can be seen from the equations of state, no remarkable anharmonic properties are expected, in the sense that the thermal pressure is well described by a linear function of temperature, i.e., αKT (where α and KT are the coefficient of thermal expansion and the isothermal bulk modulus, respectively) is virtually independent of temperature. In addition to the equations of state, we also report a unique means of holding a chemically active sample, which we established through the in situ x-ray diffraction measurements for SnI 4 at high pressures and temperatures. © 2011 American Physical Society.
  • Kazuhiro Fuchizaki, Nozomu Hamaya
    PHYSICAL REVIEW B 84 14 2011年10月 [査読有り]
     研究論文(学術雑誌) 
    The molecular crystal of tin tetraiodide is known to exhibit unusual features under pressure, such as solid-state amorphization. The low-pressure crystalline phase has a melting curve with a maximum at about 1.5 GPa, dividing the liquid phase into two states with different structures. However, the thermodynamic properties of this solid phase are still unknown. For proper thermodynamic measurements for the solid phase, we present here the Parsafar-Mason and Birch-Murnaghan-Anderson equations of state for the phase as a predecessor. The validity of the equations was confirmed by recent experimental observations. As far as can be seen from the equations of state, no remarkable anharmonic properties are expected, in the sense that the thermal pressure is well described by a linear function of temperature, i.e., alpha K-T (where alpha and K-T are the coefficient of thermal expansion and the isothermal bulk modulus, respectively) is virtually independent of temperature. In addition to the equations of state, we also report a unique means of holding a chemically active sample, which we established through the in situ x-ray diffraction measurements for SnI4 at high pressures and temperatures.
  • Kazuhiro Fuchizaki, Nozomu Hamaya, Takaki Hase, Yoshinori Katayama
    JOURNAL OF CHEMICAL PHYSICS 135 9 2011年09月 [査読有り]
     研究論文(学術雑誌) 
    We have shown from in situ synchrotron x-ray diffraction measurements that there are two thermodynamically stable liquid forms of SnI4, depending on the pressure. Based on the liquid-liquid critical point scenario, our recent measurements suggest that the second critical point, if it exists, may be located in a region close to the point at which the melting curve of the crystalline phase abruptly breaks. This region is, unlike that of water, experimentally accessible with relative ease. (C) 2011 American Institute of Physics. [doi:10.1063/1.3637038]
  • Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 2 2011年02月 [査読有り]
     研究論文(学術雑誌) 
    The pressure in an isothermal-isochoric (or constant-NVT for short) Gibbs ensemble, which consists of two coexisting phases in equilibrium as the subsystems, was derived in terms of the microscopic degrees of freedom of the ensemble. The usual virial expression for pressure was found to be valid only approximately for subsystems that compose the ensemble. Fortunately, however, application of the expression is acceptable within most of the two-phase region except in the vicinity of the critical point. This was directly confirmed by conducting the Monte Carlo simulations which generate the isothermal-isobaric (constant-NpT) Gibbs ensembles as well as the constant-NVT ones.
  • Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 2 024004 (16pages)  2010年02月 研究論文(学術雑誌) 
    A classical interaction site model is still of great value for a complex substance to which first-principles calculations are not easily applied. In simulations using file interaction site model, a tail of potential other than the Coulomb potential is usually ignored. However, such a cutoff of potential may not be justifiable under some thermodynamic conditions. or ill circumstances where precise structural and/or thermodynamic properties have to be investigated. Here, we consider I molecular system in which it molecule or an atomic cluster contains several interaction sites. These interaction sites are connected via. inverse power interactions. By attaching it virtual charge to all interaction site, all inverse power interactions, including the Coulomb interactions between true electric charges. are formally treated in a unified fashion. The periodicity introduced by the periodic boundary condition, employed ill Simulations to eliminate the effects Of surfaces, then allows LIS to adopt the idea of an Ewald Sum. thereby being free from the Cutoff. The Ewald sum is taken for the SUM of the interactions, making Use of ill, formula for the generalized zeta function proposed by the author. As all example, the potential energy of it Molecular crystal, SnI4, in the low-pressure Crystalline State, and of Solid argon is examined, where van der Waals interactions bring about cohesion in these crystals. The Lennard-Jones potential is employed to model the cohesive interaction. The treatment is extended to molecular dynamics as well. The equations Of Motion that call generate all isobaric ensemble are derived. The technical aspects when carrying Out large-scale Simulations utilizing the Ewald method are briefly mentioned.
  • Takahiro Sakagami, Kazuhiro Fuchizaki
    INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, JOINT AIRAPT-22 AND HPCJ-50 215 012123 (4pages)  2010年 研究論文(国際会議プロシーディングス) 
    The well-known Lennard-Jones potential is modified in such a way that it smoothly vanishes at a certain distance. A system whose interparticle interaction is given by such a potential is referred to as a modified Lennard-Jones system, and is served as a standard system describing simple solids and fluids. A phase diagram is determined based on the free energies obtained through thermodynamic integration.
  • Nozomu Hamaya, Fumie Matsuura, Yuki Yamagata, Kazuhiro Fuchizaki, Takaki Hase, Takahiro Sakagami, Arata Miyauchi, Takumi Kikegawa
    INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, JOINT AIRAPT-22 AND HPCJ-50 215 012079 (4pages)  2010年 研究論文(国際会議プロシーディングス) 
    Structure of the liquid forms of tin tetraiodide, SnI4, has been studied at high pressure and high temperature by synchrotron x-ray diffraction experiment. Using a new sample container, we managed to collect diffraction data with much better quality than before. The presence of two different liquid forms was verified. The structural change between these two liquid forms is expected to take place in a very narrow pressure range between 1.35 GPa at 850K and 2.03 GPa at 1000K.
  • Yuta Asano, Kazuhiro Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 5 055002 (2pages)  2009年05月 研究論文(学術雑誌)
  • Kazuhiro Fuchizaki, Takaki Hase, Akihiro Yamada, Nozomu Hamaya, Yoshinori Katayama, Ken-ichi Funakoshi
    JOURNAL OF CHEMICAL PHYSICS 130 12 121101 (4pages)  2009年03月 研究論文(学術雑誌) 
    The discovery of a first-order phase transition in fluid phosphorus aroused renewed interest in polyamorphism in liquids with a locally tetrahedral molecular structure. We have performed in situ synchrotron x-ray diffraction measurements on tin tetraiodide, which consists of SnI(4) tetrahedral molecules at ambient pressure, and established that the liquid forms existing above and below 1.5 GPa, where the slope of the melting curve of the solid phase changes abruptly, have different structures. This discovery offers evidence of thermodynamically stable polyamorphism in general compounds as well as in elements. A possible phase diagram that includes the two amorphous states already found is proposed based on the pseudobinary regular solution model. The vertex-to-face orientation between the nearest molecules plays a key role in the transition from the low-pressure to the high-pressure liquid phase.
  • Kazuhiro Fuchizaki, Takeshi Nakamichi, Hiroyuki Saitoh, Yoshinori Katayama
    SOLID STATE COMMUNICATIONS 148 9-10 390 - 394 2008年12月 研究論文(学術雑誌) 
    Diffraction data from hexagonal boron nitride compiled through in situ synchrotron x-ray measurements under pressures and temperatures up to about 8 GPa and 1000 K, respectively, were analyzed in the light of Birch-Murnaghan's and Parsafar-Mason's equations of state. The isothermal bulk moduli at ambient conditions obtained from these equations almost coincide. However, the value, about 20 GPa, is appreciably small compared to the one reported previously. The x-ray diffraction patterns by which the current result is justified are presented. The possible origin of a large discrepancy in the values is discussed. (C) 2008 Elsevier Ltd. All rights reserved.
  • Kazuhiro Fuchizaki, Shinji Kohara, Yasuo Ohishi, Nozomu Hamaya
    JOURNAL OF CHEMICAL PHYSICS 127 6 064504-1 - 064504-8  2007年08月 研究論文(学術雑誌) 
    Synchrotron x-ray diffraction measurements were performed on liquid SnI4 up to a scattering vector of 25 A(-1), utilizing a horizontal two-axis diffractometer installed at the SPring-8 bending magnet beam line BL04B2 in Japan. An effective method based on the maximum entropy method was devised to transform the measured total structure factor to the reduced radial distribution function. The reliability of the density estimation is discussed.(c) 2007 American Institute of Physics.
  • K Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 3 034601-1-034601-4  2006年03月 研究論文(学術雑誌) 
    The expression known as Murnaghan's equation of state in high-pressure research community is mathematically a correct solution to the equation of bulk modulus but is valid only within a very limited parameter space. Moreover, the equation of state in question exhibits a peculiar behavior at high pressures when fitted to compression data. An alternative expression with a much wider range of validity is given. No peculiarity appears in the resultant compression curve. The latter expression thus provides a new tool as an infinitesimal-strain equation of state for quick estimate of compression characteristics of substances.
  • K Fuchizaki, K Nagai
    SOLID STATE COMMUNICATIONS 132 5 305 - 308 2004年11月 研究論文(学術雑誌) 
    A recent experimental investigation into the low-pressure crystalline state of an SnI4 molecular crystal under high pressure has revealed that the melting points predicted from molecular dynamics simulations were too high. The short-range octupole-octupole intermolecular interaction, which plays an important role at high pressures, was newly introduced to the model to accommodate this effect. These interactions do indeed destabilize the crystalline state. However, the degree of destabilization was too small to quantitatively reproduce the experimental melting points. A possible origin of the discrepancy is discussed. (C) 2004 Elsevier Ltd. All rights reserved.
  • K Fuchizaki, Y Fujii, Y Ohishi, A Ohmura, N Hamaya, Y Katayama, T Okada
    JOURNAL OF CHEMICAL PHYSICS 120 23 11196 - 11199 2004年06月 研究論文(学術雑誌) 
    The location of the liquidus in the low-pressure crystalline phase of SnI4 was determined utilizing in situ x-ray diffraction measurements under pressures up to approximately 3.5 GPa. The liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes almost flat. The results are compared to those from molecular dynamics simulations. Ways to improve the model potential adopted in the simulations are discussed. (C) 2004 American Institute of Physics.
  • K Fuchizaki, K Kawasaki
    JOURNAL OF PHYSICS-CONDENSED MATTER 14 46 12203 - 12222 2002年11月 研究論文(学術雑誌) 
    Glassy dynamics of fluid particles in a supercooled liquid is discussed on the basis of the time-evolution equation obtained through the dynamical density functional theory (DDFT). The advantage, brought about by the coarse-grained nature of the formalism, in treating such strongly correlated motion over other approaches, such as the mode-coupling theories and direct computer simulations, is emphasized. A direction in which the DDFT should prove its worth on examining the phenomena is suggested.
  • K Fuchizaki, S Sugiyama, Y Fujii
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 5 1321 - 1326 2001年05月 研究論文(学術雑誌) 
    Isothermal-isobaric molecular dynamics simulations were carried out for SnI4 in its liquid state under hydrostatic pressure up to about 5 GPa. The equation of state was obtained from the virial pressure. which was found to be in good agreement with that derived by Boublik regarding a system consisting of hard-convex bodies as a reference fluid. The virial coefficients determined from the equation of state were presented so as to facilitate experimental confirmation.
  • T Nagai, K Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 9 2727 - 2730 2000年09月 研究論文(学術雑誌) 
    The relaxation process to a scaling state which is a nonequilibrium steady state in evolving cellular structures, such as soap froths and grain systems, is investigated by computer simulation of the vertex model and phenomenology in two dimensions. Our results are as follows: (i) This relaxation is hierarchical, that is, the average size of a cell (the characteristic length of the system) relaxes rapidly at an early stage and then topological quantities associated with the shape of cells relax slowly at a late stage. (ii) The latter slow relaxation is well described by the stretched exponential function. (iii) The time exponent beta of the stretched exponential function is related to the power gamma of the distribution for the time interval of the topological change in the form gamma = 1 + beta.
  • K Fuchizaki, S Sugiyama, Y Fujii
    JOURNAL OF CHEMICAL PHYSICS 112 23 10379 - 10390 2000年06月 研究論文(学術雑誌) 
    The pressure-temperature phase diagram of SnI4 was investigated to examine the inherent instability of crystalline SnI4 in terms of undergoing pressure-induced solid state amorphization, by conducting molecular dynamics simulations prior to studies involving laboratory experiments. The SnI4 molecules are regarded as rigid tetrahedra interacting with one another via van der Waals forces. In order for the isothermal-isobaric ensemble to be achieved, the well-established Nose-Klein scheme combined with the momentum scaling method was adopted when carrying out the simulations. The system was carefully heated up under fixed hydrostatic pressure from the low-pressure crystalline state across the melting point, which was determined by monitoring the time-dependence of the mean square displacement of the molecules, whereas, on cooling, the liquid state remained supercooled down to room temperature. The slope of the liquidus in the phase diagram between the low-pressure crystalline phase and the liquid phase was found to be positive, implying that the low-pressure crystalline phase has little connection with solid state amorphization. An expected overall pressure-temperature phase diagram of SnI4 is discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)50923-4].
  • K Fuchizaki
    JOURNAL DE PHYSIQUE IV 10 P7 37 - 40 2000年05月 研究論文(学術雑誌) 
    Strongly correlated dynamics of fluid particles in a supercooled liquid is discussed on the basis of the mesoscopic kinetic equation involved in the dynamical density functional theory, focusing attention on the advantage of a spatio-temporally coarse-grained description. By virtue of the coarse-grained character, the time evolution of the density profile is effectively obtainable beyond the late beta-relaxation regime, skipping over microscopic processes. Application of the theory is proposed in discussing the correlation length of particle motion, which may be crucial in examining the effect of confinement.
  • K Fuchizaki, S Sugiyama, Y Fujii
    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT 138 138 264 - 265 2000年 研究論文(学術雑誌) 
    Isothermal-isobaric molecular dynamics simulations for molecular crystal SnI4 are performed to examine the thermodynamic stability of the low-pressure crystalline phase against melting. Radial distribution functions in the liquid state are presented which await experimental verification.
  • K Tanaka, K Fuchizaki
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 60 8-9 1237 - 1240 1999年08月 研究論文(学術雑誌) 
    The crossover behavior from collective to local spin motions in diluted antiferromagnets is discussed using the canonical molecular dynamics method without introducing any ad hoc approximations to the equations of motion. The calculated dynamic responses are compared with the recent results obtained by neutron inelastic scattering experiments. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • K Fuchizaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 8 2864 - 2865 1999年08月 研究論文(学術雑誌)
  • K Fuchizaki, K Kawasaki
    PHYSICA A 266 1-4 400 - 412 1999年04月 研究論文(学術雑誌) 
    Slow dynamics which shows up in supercooled liquid near the glass transition is discussed on the basis of the discretized version of the dynamical density functional equation which is the mesoscopic kinetic equation put forth recently in an attempt to go beyond the current mode-coupling theories. The discretization was realized through an appropriate mapping of the equation onto the kinetic lattice gas model in such a way that the master equation for the latter could approximately lead to the former upon coarse-graining of the spatio-temporal scales. The kinetic lattice gas model, which contains no ad hoc parameters except the direct correlation function of the reference liquid, is then solved for a hard-sphere liquid by using the ordinary Monte Carlo method to give successfully the thermally activated hopping process which is dominant at later times. Aspect of the free-energy landscape is also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.
  • K Fuchizaki, K Kawasaki
    SLOW DYNAMICS IN COMPLEX SYSTEMS 469 553 - 554 1999年 [査読有り]
     研究論文(国際会議プロシーディングス)
  • T Nagai, K Fuchizaki
    SLOW DYNAMICS IN COMPLEX SYSTEMS 469 303 - 304 1999年 [査読有り]
     研究論文(国際会議プロシーディングス)
  • K Kawasaki, K Fuchizaki
    JOURNAL OF NON-CRYSTALLINE SOLIDS 235 57 - 65 1998年08月 研究論文(学術雑誌) 
    The current mode coupling theory (MCT) of supercooled liquids and glass transition appears to be limited to the initial stage of freezing prior to glass transition despite its remarkable successes. In the hope of overcoming this limitation a theoretical framework is proposed which combines the mode coupling mechanism and the free energy barrier hopping which takes place in the glassy state. The new theory takes the form of a Fokker-Planck type equation for the probability distribution functional of density. The theory can be mapped onto a kinetic Ising model and some numerical consequences will be presented. (C) 1998 Elsevier Science B.V. All rights reserved.
  • K Fuchizaki, K Kawasaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 7 2158 - 2161 1998年07月 研究論文(学術雑誌) 
    Through the mapping onto the kinetic lattice gas model the dynamical density functional equation is solved by the Monte Carlo method in a deeply supercooled hard-sphere liquid, while focusing on how the system explores the free-energy landscape during a relaxation process. A variety of metastable states appear as the supercooling proceeds beyond the equilibrium crystallization point. Our approach is the first to reproduce the hopping transitions among these states as a solution of a mesoscopic kinetic equation.
  • K Fuchizaki, K Kawasaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 5 1505 - 1508 1998年05月 研究論文(学術雑誌) 
    The dynamical density functional equation put forth recently in an attempt to go beyond the current mode coupling theories of supercooled liquid and glass transitions is solved by mapping to the kinetic lattice gas model. Analyses of the dynamic structure factor in the initial stage of freezing reveal that the equation correctly captures the mode coupling mechanism of density fluctuations.
  • T Nagai, K Fuchizaki
    GRAIN GROWTH IN POLYCRYSTALLINE MATERIALS III 161 - 166 1998年 [査読有り]
     研究論文(国際会議プロシーディングス) 
    Relaxation to a scaling state in grain growth has been investigated by computer simulation of the two-dimensional vertex model which expresses a grain system with small number of degrees of freedom. Two kinds of grain boundaries with low and high energies are taken into account. Starting with a random pattern, the system develops to coarsen and approaches a scaling state with the statistical self-similarity after long time. This relaxation process is found to be hierarchical, i.e. the average grain size first follows a power law of time and then other quantities, such as the variances of grain size and edge number distributions, gradually approach constants. It is shown that the latter slow relaxation is well described by the stretched exponential form which is defined by an inverse of exponential of time to a power less than one and is widely observed in amorphous materials. The origin of this slow relaxation is discussed by tracing each life of grain to find the relation between its topological change and the slow relaxation. It is concluded that this slow relaxation can be qualitatively explained by the defect diffusion model.
  • K Fuchizaki
    GRAIN GROWTH IN POLYCRYSTALLINE MATERIALS III 503 - 508 1998年 [査読有り]
     研究論文(国際会議プロシーディングス) 
    Recently large-scale numerical computations, including the first principles calculations, regarding the interfacial energy between the two crystallines, which capture microscopic nature of materials concerned have been made. It has been believed that the details of the bonding at an interface are crucial in understanding the dependence of the interfacial energy on geometrical location of the interface. Nevertheless the similarity of the overall features of the curves of the interfacial energy obtained against variation of the parameters which specify the geometrical location of an interface for several materials suggests a common underlying physics which should not depend strongly on the material chosen. The present investigation is therefore to discuss the commonly observed characteristics in the energy curves from purely geometrical point of view. To this end I first clarify, taking the twist boundaries as an example to which the method is applied, the hierarchy in the geometrical construction of the coincident-site lattice by invoking the continued-fraction expansion algorithm for the transformation operator between the two lattice structures which are separated by the interface in question. Interfacial energies are then calculated against misorientation based on a two-dimensional version of the model put forth by du Plessis and van der Merwe, which turn out to reveal a fractal energy surface with cusps at every Sigma value. It is emphasized that these singularities are not attributable to the nature of the bonding but are of purely geometrical origin.
  • N Hamaya, K Sato, K UsuiWatanabe, K Fuchizaki, Y Fujii, Y Ohishi
    PHYSICAL REVIEW LETTERS 79 23 4597 - 4600 1997年12月 研究論文(学術雑誌) 
    Synchrotron x-ray diffraction study establishes a novel structure sequence in SnI4 at high pressures to 153 GPa. A new crystalline phase responsible for the metallization is observed above 7.2 GPa. The pressure-amorphized SnI4 emerging above 15 GPa crystallizes at 61 GPa into another new structure having an apparent fee lattice with a nearest-neighbor distance as short as 3.00 Angstrom. This provides evidence for the occurrence of molecular dissociation. Atomic arrangement in the nonmolecular phase and structural properties of the amorphous state an discussed.
  • K Fuchizaki, M Isobe, Y Fujii, K Sato, N Hamaya
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 6 1575 - 1578 1997年06月 研究論文(学術雑誌) 
    Isothermal-isobaric molecular dynamics simulations of molecular crystal SnI4 are carried out based on a model consisting of rigid tetrahedral molecules interacting via van der Waals forces. The hehavior of the crystal upon an increase in pressure is satisfactorily reproduced on both microscopic and macroscopic scales in the pressure regime in which the low-pressure phase is stable. In particular the compression curve obtained is in excellent agreement with the experimentally determined one. Upon further increase in pressure, however. no symmetry change is detected in the present simulations over the pressure regime in which the phase transformation and the subsequent solid state amorphization are experimentally found to take place.
  • Molecular Dynamics Simulation Study of the Behavior of Molecular Crystal Tin Tetraiodide under Hydrostatic Pressure (共著)
    Kazuhiro Fuchizaki, Masaharu Isobe, Yasuhiko Fujii, Kyoko Sato, Nozomu Hamaya
    Technical Report of ISSP Ser.A 3262 1 - 4 1997年04月 研究論文(大学,研究機関等紀要)
  • Y Kuroiwa, A Konishi, T Shobu, Y Noda, K Fuchizaki, Y Morii, Y Yamada, HR Child, H Chou, SC Moss
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 4 1033 - 1043 1997年04月 研究論文(学術雑誌) 
    Neutron scattering studies have been performed to elucidate the martensitic transformation mechanism in a quenched Cu61Zn39 alloy. The TA(1)[110] phonon branch (e//[1 (1) over bar 0]) showed slight softening over the entire q-region in the parent phase as the transformation temperature was approached on cooling. No particular dip was observed even just above the transformation temperature, while the intensities of the quasi-elastic diffuse scattering developed near q = 1/6[1 (1) over bar 0] and 1/3[1 (1) over bar 0] positions in the parent phase. No anomaly was found in several other phonon branches. The structure of the beta(1) '' martensite phase was investigated, and a mixed phase of an orthorhombic structure and a monoclinic structure is proposed, which are both different from the previously reported structures. An annealing effect was observed to confirm the role of inclusions in the parent phase.
  • K Kawasaki, K Fuchizaki, S Miyazima
    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT 126 126 305 - 308 1997年 研究論文(学術雑誌) 
    Kinetic Ising model mapped from the dynamical density functional theory for dense fluid is simulated by the Monte Carlo method. This permits long time simulations which enable us to go over from relatively lower density fluid regions to high density freezing regions without difficulty.
  • T Nagai, K Fuchizaki
    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT 126 126 111 - 114 1997年 研究論文(学術雑誌) 
    Relaxation of domain structures (soap foam, grain aggregate, etc.) to a scaling state has been investigated by computer simulation. Our result is as follows: this relaxation has a hierarchical structure, i.e., the average domain size first relaxes and then the average domain shape relaxes slowly. The latter can be well described by the Kohlrausch anomalous relaxation law. The relation between the two relaxations is also discussed.
  • K Fuchizaki, K Kawasaki
    GRAIN GROWTH IN POLYCRYSTALLINE MATERIALS II, PTS 1 AND 2 204- 267 - 278 1996年 研究論文(学術雑誌) 
    A significant step forward has been achieved in computer modeling of time-evolution of three-dimensional grain aggregates, by projecting the equation of motion for the grain boundaries with continuous degrees of freedom into that of grain vertices, thus leaving a finite set of equations of motion for vertices. This model is referred to as the vertex model. It is noted that such a coarse-graining can be carried out not in ad-hoc manner but in such a way that the grain edges are approximated by straight lines in the course of projecting out unimportant continuous degrees of freedom. However, we are immediately confronted with the fact that the grain faces bounded by these straight edges are not always planar in general which is characteristic of three-dimensional cellular systems. To circumvent this difficulty supplementary vertices called virtual vertices are introduced on grain faces by which a unique triangulation of the faces can be achieved. The actual introduction of virtual vertices, which should still be simple enough to be practically implemented, has been performed in the following two ways; (i) Take the positions of virtual vertices as the centers of gravity of each grain face (center-of-gravity model). (i) Take the initial positions of virtual vertices as the centers of gravity as in (i), but their subsequent motions are determined selfconsistently by the equations of motion (virtual-vertex model). Equations of motions of vertices are then readily derived for each case. Note here that some lower cutoff resolution below which the movement of vertices cannot be described by the equations of motion does exit because of the coarse-grained character of the vertex models. Such movements occurring in very limited spatial regions can be adequately described by local topology changes which can always be resolved into recombination processes between the two grains and/or tetrahedron annihilation process. In this way, dynamics of grain aggregates can be unambiguously described by the set of equations of motion for all the vertices together with the elementary topological processes. The model permits further refinements of arbitrary degree by increasing the number of virtual vertices in appropriate manner. Grain growth kinetics is discussed on the basis of the vertex model by comparing the results obtained by the vertex model simulations with those obtained by the Potts model simulations.
  • K FUCHIZAKI, K KAWASAKI
    PHYSICA A 221 1-3 202 - 215 1995年11月 研究論文(学術雑誌) 
    An effective computer modeling of time evolution of three-dimensional cellular systems like soap froths and crystalline grain aggregates has been devised, which captures the essence of difficult correlation effects of neighboring cells. This can be achieved by eliminating the continuous degrees of freedom besides the immediate vicinity of the center of a singular region of space, that is, an intersection of interfaces from the original full-curvature driven equation of motion of interfaces, thus leaving a set of equations of motion for such intersections, i.e. vertices. To actually carry out this projection operation each interface is divided into a set of two-dimensional simplexes. A derivation of the model equations is given in the most general possible form. Various results including topological characteristics of three-dimensional cellular patterns were obtained using the simpler version of these vertex equations, among which the result for the average growth rate of f-sided cells is presented. An application to some specific cellular systems is also discussed.
  • K FUCHIZAKI, T KUSABA, K KAWASAKI
    PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES 71 3 333 - 357 1995年03月 研究論文(学術雑誌) 
    The time evolution of three-dimensional cellular patterns is discussed on the basis of the vertex model which consists of a set of equations for the motion of vertices obtained from the full curvature-driven equation of motion of cell boundaries (faces) by a reduction in the degrees of freedom. Some difficulty in the earlier vertex models, originating from the fact that faces are non-coplanar, is now side-stepped by introducing virtual vertices as supplementary degrees of freedom. Equations of motion are then readily derived assuming that the whole process is purely dissipative. By solving these equations numerically, scaling properties concerning cellular pattern growth are obtained. In addition, geometrical features such as the three-dimensional versions of the Aboav-Weaire law and the Lewis law are verified with fair accuracy. We emphasize that our vertex model has the potentiality for efficient improvements of indefinite degree by introducing arbitrary numbers of virtual vertices.
  • Kazuhiro Fuchizaki, Takuo Kusaba, Kyozi Kawasaki
    Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties 71 3 333 - 357 1995年 [査読有り]
     研究論文(学術雑誌) 
    The time evolution of three-dimensional cellular patterns is discussed on the basis of the vertex model which consists of a set of equations for the motion of vertices obtained from the full curvature-driven equation of motion of cell boundaries (faces) by a reduction in the degrees of freedom. Some difficulty in the earlier vertex models, originating from the fact that faces are non-coplanar, is now side-stepped by introducing virtual vertices as supplementary degrees of freedom. Equations of motion are then readily derived assuming that the whole process is purely dissipative. By solving these equations numerically, scaling properties concerning cellular pattern growth are obtained. In addition, geometrical features such as the three-dimensional versions of the Aboav-Weaire law and the Lewis law are verified with fair accuracy. We emphasize that our vertex model has the potentiality for efficient improvements of indefinite degree by introducing arbitrary numbers of virtual vertices. © 1995 Taylor & Francis Group, LLC.
  • K FUCHIZAKI
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 63 11 4051 - 4059 1994年11月 研究論文(学術雑誌) 
    A procedure is discussed concerning numerical lattice sums of quantities characterized by inverse power law and modulation wave vector. A relatively simple formula for the sum is derived for odd-dimensional lattice but for arbitrary power, modulation wave vector as well as lattice structure, which includes the sum of such as the Ruderman-Kittel-Kasuya-Yosida and the Friedel interactions as one of the special cases.
  • K FUCHIZAKI
    INTERNATIONAL JOURNAL OF MODERN PHYSICS B 8 15 1989 - 2019 1994年07月 研究論文(学術雑誌) 
    A frustrated vertex model is proposed to elucidate some essential properties in proton glass. The frustration mechanism is clarified which arises from the geometric constraint, the so-called ice rule, rather than competing ferroelectric and antiferroelectric interactions. By comparing two order parameters which are obtained by exact thermal averaging and by Monte Carlo sampling, broken ergodicity as well as broken symmetry is examined. Estimation of the diffusion constant in a diffusion process in relevant configuration space allows us to discuss the ergodic convergence property in connection with the free energy surface structure.
  • T NAGAI, K FUCHIZAKI, K KAWASAKI
    PHYSICA A 204 1-4 450 - 463 1994年03月 研究論文(学術雑誌) 
    The effect of crystal orientation of grains on grain growth is investigated by computer simulation. A vertex model which includes the orientation dependence of grain boundary energy is used. It is shown that the orientation effect gives rise to more distortion and more diversity in the shape of the grains. Such a distortion in the shape of grains is measured by the moment tensor, for a quantitative discussion. It is also found that the 1/2-power growth law of the average size of grains still holds under such an anisotropic circumstance.
  • K FUCHIZAKI
    PHILOSOPHICAL MAGAZINE LETTERS 67 6 385 - 391 1993年06月 研究論文(学術雑誌) 
    The continued-fraction expansion algorithm is utilized to clarify the hierarchy among the coincident-site lattice structures. Boundary energies are calculated against twist misorientation based on a two-dimensional version of the model suggested by du Plessis and van der Merwe in 1965, which reveal a fractal energy surface with cusps at very SIGMA value. The origin of the cusps and the effects of local structural relaxation on the boundary energies are discussed.
  • K KAWASAKI, T NAGAI, T OKUZONO, K FUCHIZAKI
    MODELING OF COARSENING AND GRAIN GROWTH 295 - 310 1993年 [査読有り]
     研究論文(国際会議プロシーディングス)
  • A NAGASAWA, A KUWABARA, Y MORII, K FUCHIZAKI, S FUNAHASHI
    Materials Transaction Japan Institute of Metals 33 3 203 - 207 1992年03月 研究論文(学術雑誌) 
    The ultrasonic pulse echo method and the X-ray and neutron diffraction methods have been used to investigate the lattice instability of the premartensitic beta-1 phase of a Cu-27.0Al-5.5Pd alloy under uniaxial pressure. The third order elastic constants and the [110]TA1 mode Grueneisen parameter show that the beta-1 phase is strongly anharmonic. This situation causes marked instability of the beta-1 phase toward the (110)[110BAR] shear under the [001] pressure. Such an instability also appears as a gradient change of the [110]TA1 phonon dispersion relation at the GAMMA-point (q = 0). Interplanar force constant analysis of the [110]TA1 phonon dispersion relations suggests that the martensite induced by the [001] pressure would have the 18R (or 9R) structure. The 2/3[110]q(max) diffraction anomaly is found only by neutron diffraction and it does not show any noticeable pressure dependence; the anomaly is not the precursor of the stress-induced martensitic transformation.
  • Y MIYAZAKI, H YAMANE, T KAJITANI, T OKU, K HIRAGA, Y MORII, K FUCHIZAKI, S FUNAHASHI, T HIRAI
    PHYSICA C 191 3-4 434 - 440 1992年02月 研究論文(学術雑誌) 
    Sr2CuO2(CO3) were prepared at 1273 K and 0.01 MPa CO2 partial pressure in a flowing gas of O2-CO2 using a mixture of SrCO3 and CuO powders as a starting material. The compound has a tetragonal structure with lattice constants a = 7.8045(1), and c = 14.993(1) angstrom, and its space group is I4. The formula per unit cell is 8 Sr2CuO2(CO3), and measured and calculated densities are D(m) = 4.71 g/cm3, and D(x) = 4.81 g/cm3, respectively. The crystal structure was refined by Rietveld analysis on X-ray powder diffraction and neutron powder diffraction data. The final residuals (R(F)) were 4.31 and 4.27% for the X-ray and neutron data, respectively. The structure consists of deformed [CuO6] octahedrons and layers of ordered triangular CO3 groups. Sr atoms having eight near oxygen neighbors are between the [CuO6] octahedrons and the CO3 layers.
  • T KAJITANI, Y KITAGAKI, K HIRAGA, S HOSOYA, T FUKUDA, Y YAMAGUCHI, S WADA, S SUGAI, Y MORII, K FUCHIZAKI, S FUNAHASHI
    PHYSICA C 185 579 - 580 1991年12月 研究論文(学術雑誌) 
    Present work is aimed to obtain a clear idea of the phase stabilities of the title oxide at temperatures from 10K to 900K. X-ray powder and single-crystal diffraction measurements and neutron high-resolution powder diffraction measurements were carried out for the samples annealed in several different atmospheres i.e. CO + CO2 or O2 + Ar mixed gas, air, vacuum at about 10(-3)Pa. Clear evidence that NiO6 octahedrons rotate in the bc-plane (b > c > a setting) in La2NiO4.00 at room temperature was obtained. Shape of a magnetic peak 011 shows some broadening at temperatures below 70K i.e. LTO2 range.
  • A NAGASAWA, K KITA, Y MORII, K FUCHIZAKI, S KATANO, S FUNAHASHI, HR CHILD
    Materials Transaction Japan Institute of Metals 32 11 1011 - 1016 1991年11月 研究論文(学術雑誌) 
    The present study by X-ray and neutron diffraction methods is concerned with the omega-like peak appearing at the positions (H +/- 2/3, K +/- 2/3, L +/- 4/3) and (H +/- 2/3, K +/- 2/3, L -/+ 4/3) in the reciprocal lattice of the quenched beta(1) phase with the Heusler type structure of AuCuZn2. The obtained results indicate evidently that the omega-like peak is neither due to the omega phase formation as is the case of Zr alloy nor precursor phenomenon of the martensitic transformation. It is originated from a certain kind of regular arrangement of vacancies in the incompletely ordered B2 phase: the vacancies are responsible for the ordering reaction to the Heusler type structure occurring at about 670 K. They are frozen into the Heusler phase formed by quenching, and hence the quenched Heusler phase exhibits the omega-like peak as observed. The peak disappears with vacancy annihilation from the Heusler type beta(1) phase. Characteristics of both the [111]LA and [112BAR]TA phonon dispersion relations also support this conclusion.
  • Y YAMADA, Y NODA, K FUCHIZAKI
    PHYSICAL REVIEW B 42 16 10405 - 10414 1990年12月 研究論文(学術雑誌)
  • Y YAMADA, K FUCHIZAKI
    PHYSICAL REVIEW B 42 15 9420 - 9428 1990年11月 研究論文(学術雑誌)
  • An embryo-Phonon Coupling Model for Martensitic Phase Transformation in BCC-Alloys
    Materials Science Forum 56-58 107 - 112 1990年
  • Structure Analysis of NiAl Martesite
    Material Science Forum 56-58 299 - 304 1990年
  • Search for polytipic structures of gadolinium
    High Pressure Research 4 375 - 377 1990年
  • K FUCHIZAKI, Y YAMADA
    PHYSICAL REVIEW B 40 7 4740 - 4748 1989年09月 研究論文(学術雑誌)
  • K FUCHIZAKI, Y NODA, Y YAMADA
    PHYSICAL REVIEW B 39 13 9260 - 9266 1989年05月 研究論文(学術雑誌)
  • E MATSUSHITA, K FUCHIZAKI
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 26 793 - 794 1987年 研究論文(学術雑誌)

書籍

  • 新物理小事典
    渕崎 員弘 (担当:分担執筆)
    三省堂 2009年06月 ISBN: 9784385240176 468
  • 古典力学(下)
    渕崎 員弘 (担当:共訳)
    吉岡書店 2009年03月 ISBN: 9784842703503 852
  • 古典力学(上)
    渕崎 員弘 (担当:共訳)
    吉岡書店 2006年07月 ISBN: 9784842703367 485
  • Slow Dynamics in Complex Systems
    American Institute of Physics 1999年
  • Slow Dynamics in Complex Systems
    American Institute of Physics 1999年
  • Slow Dynamics in Complex Systems
    American Institute of Physics 1999年
  • Slow Dynamics in Complex Systems
    American Institute of Physics 1999年
  • Grain Grwoth in Polycrystalline Materials III
    TMS publication 1998年
  • Grain Grwoth in Polycrystalline Materials III
    TMS publicationGrain Growth in Polycrystalline Materials (]G0003[) 1998年
  • Grain Grwoth in Polycrystalline Materials III
    TMS publication 1998年
  • Grain Grwoth in Polycrystalline Materials III
    TMS publicationGrain Growth in Polycrystalline Materials (]G0003[) 1998年
  • Modeling of coarsening and grain growth
    TMS publication 1993年
  • Proceedings of International Conferenece on Comupter-assisted Materials Design and Process Simulation
    Iron and Steel Institute of JapanProceedings of International Conference on Computer-assisted Materials Design and Process Simulation 1993年
  • Proceedings of International Conferenece on Comupter-assisted Materials Design and Process Simulation
    Iron and Steel Institute of JapanProceedings of International Conference on Computer-assisted Materials Design and Process Simulation 1993年
  • Proceedings of International Conferenece on Comupter-assisted Materials Design and Process Simulation
    Iron and Steel Institute of JapanProceedings of International Conference on Computer-assisted Materials Design and Process Simulation 1993年
  • Proceedings of the Fifth International Symposium on Advanced Nuclear Energy Research
    Japan Atomic Energy Research InstituteProc. of the Fifth International Symposium on Advanced Nuclear Energy Research 1993年
  • Proceedings of the Fifth International Symposium on Advanced Nuclear Energy Research
    Japan Atomic Energy Research InstituteProc. of the Fifth International Symposium on Advanced Nuclear Energy Research 1993年
  • Modeling of coarsening and grain growth
    TMS publication 1993年
  • Proceedings of International Conferenece on Comupter-assisted Materials Design and Process Simulation
    Iron and Steel Institute of JapanProceedings of International Conference on Computer-assisted Materials Design and Process Simulation 1993年
  • Proceedings of International Conferenece on Comupter-assisted Materials Design and Process Simulation
    Iron and Steel Institute of JapanProceedings of International Conference on Computer-assisted Materials Design and Process Simulation 1993年
  • Proceedings of International Conferenece on Comupter-assisted Materials Design and Process Simulation
    Iron and Steel Institute of JapanProceedings of International Conference on Computer-assisted Materials Design and Process Simulation 1993年
  • Proceedings of the Fifth International Symposium on Advanced Nuclear Energy Research
    Japan Atomic Energy Research InstituteProc. of the Fifth International Symposium on Advanced Nuclear Energy Research 1993年
  • Proceedings of the Fifth International Symposium on Advanced Nuclear Energy Research
    Japan Atomic Energy Research InstituteProc. of the Fifth International Symposium on Advanced Nuclear Energy Research 1993年
  • Proceedings of the Fourth International Symposium on Advanced Nuclear Energy Research
    Japan Atomic Energy Research Institute 1992年
  • Mechanism of Superconductivity
    JJAP Seriest Mechanisms of Super conductivity 1992年
  • Proceedings of the Fourth International Symposium on Advanced Nuclear Energy Research
    Japan Atomic Energy Research Institute 1992年
  • Mechanism of Superconductivity
    JJAP Seriest Mechanisms of Super conductivity 1992年

講演・口頭発表等

  • 渕崎員弘, 大村彩子, 兵頭友樹, 成田博貴, 尾原幸治
    日本物理学会2020年秋季大会 2020年09月 口頭発表(一般)
  • 渡邊佳, 渕崎員弘
    日本物理学会2020年秋季大会 2020年09月 口頭発表(一般)
  • 渕崎員弘
    日本物理学会第75回年次大会 2020年03月 口頭発表(一般)
  • Kazuhiro Fuchizaki
    Joint Polish-German Crystallographic Meeting 2020 2020年02月 口頭発表(一般)
  • Kazuhiro Fuchizaki
    The 57th European High Pressure Research Group Meeting on High Pressure Science and Technology 2019年09月 口頭発表(一般)
  • A probable polymerization process on the liquid-to-liquid crossover in GeI4  [通常講演]
    渕崎 員弘
    26th Sitges Conference on Statistical Mechanics 2019年05月 口頭発表(一般)
  • Is GeI4’s liquid-liquid transition identifiable as a percolation transition of `bonds’?  [通常講演]
    渕崎 員弘
    27th Annual Meeting of the German Crystallographic Society 2019年03月 ポスター発表
  • ヨウ化錫やヨウ化ゲルマニウム系の液−液転移前駆現象としての分子低対称化  [通常講演]
    渕崎 員弘
    日本物理学会 第74回年次大会 2019年03月 口頭発表(一般)
  • 液体GeI4の圧力誘起構造変化  [通常講演]
    渕崎 員弘
    2018年度量子ビームサイエンスフェスタ 2019年03月 ポスター発表
  • Pressure-induced local symmetry breaking upon liquid-liquid transition of GeI4 and SnI4  [通常講演]
    渕崎 員弘
    The 56th European High Pressure Research Group Meeting on High Pressure Science and Technology 2018年09月 口頭発表(一般)
  • A critical-point scenario for the liquid-liquid transition of tin tetraiodide  [通常講演]
    渕崎 員弘
    35th International Conference on Solution Chemistry (ICSC 2018) 2018年08月 口頭発表(一般)
  • 変形Lennard-Jones系のスピノーダル  [通常講演]
    渕崎 員弘
    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の今と未来」 2018年04月 ポスター発表
  • ヨウ化錫の液-液転移シナリオ  [通常講演]
    渕崎 員弘
    日本物理学会 第73回年次大会 2018年03月 シンポジウム・ワークショップパネル(指名)
  • Pressure-induced structural crossover in liquid GeI4  [通常講演]
    渕崎 員弘
    UPC Seminar 2018年03月 公開講演,セミナー,チュートリアル,講習,講義等
  • Detecting the structural change and density anomaly in liquid iodides by in-situ synchrotron x-ray diffraction and absorption measurements under high pressures  [通常講演]
    渕崎 員弘
    26th Annual Meeting of the German Crystallographic Society (DGK) 2018年03月 ポスター発表
  • Liquid—liquid transition in GeI4  [通常講演]
    渕崎 員弘
    The 55th European High Pressure Research Group Meeting on High Pressure Science and Technology 2017年09月 口頭発表(一般)
  • ヨウ化錫の液-液転移シナリオ  [招待講演]
    渕崎 員弘
    分子研研究会「不均一なゆらぎとその周辺の科学:Nishikawa Line から第二臨界点まで」 2017年07月 口頭発表(一般)
  • SnI4—the substance that allows us to enter the no man’s land  [通常講演]
    渕崎 員弘
    WaterSpain 2017 2017年07月 口頭発表(一般)
  • 相境界決定のための高効率2-相シミュレーションの提案  [通常講演]
    渕崎 員弘
    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の今と未来」 2017年04月 ポスター発表
  • 簡易型6-6フレームの試作と評価試験  [通常講演]
    渕崎 員弘
    量子ビームサイエンスフェスタ 2017年03月 ポスター発表
  • 渕崎 員弘
    42nd Conference of the Middle-European Cooperation in Statistical Physics 2017年02月 ポスター発表 Lyon, France
  • ヨウ化錫系における第二臨界点存在の立証  [通常講演]
    渕崎 員弘
    日本物理学会秋季大会 2016年09月 口頭発表(一般)
  • 1.5GPa付近でのヨウ化錫液体構造の精査  [通常講演]
    渕崎 員弘
    日本物理学会秋季大会 2016年09月 口頭発表(一般)
  • ヨウ化錫流体相での密度極大の検出  [通常講演]
    渕崎 員弘
    日本物理学会秋季大会 2016年09月 口頭発表(一般)
  • 渕崎 員弘
    The 54th European High Pressure Research Group (EHPRG) International Meeting on High Pressure Science and Technology 2016年09月 口頭発表(一般) Bayreuth, Germany
  • 渕崎 員弘
    26th IUPAP International Conference on Statistical Physics 2016年07月 口頭発表(一般) Lyon, France

作品等

  • 液相および非晶質状態内の相転移と新たな臨界現象
    2006年 -2007年
  • 分子性液体構造に関する理論的研究
    2005年 -2005年
  • 液体構造に関する理論的研究
    2005年 -2005年
  • ヨウ化錫液体における液相-液相転移
    2003年 -2004年
  • 圧力誘起非晶質化現象の解明
    2003年 -2003年
  • ヨウ化錫低圧結晶相の融解曲線
    2002年 -2002年
  • 時間発展するセルパターンにおける遅い緩和
    1997年
  • Slow Relaxation in Evolving Cellular Structures
    1997年
  • 四面体分子系の構造緩和過程
    1996年
  • Structural Relaxation in Nonspherical Molecular Fluids
    1996年

MISC

  • 渕崎 員弘 日本結晶学会誌 記事・総説・解説・論説等(学術雑誌) 58 42 -47 2016年03月 [査読有り][招待有り]
  • Nonequilibrium Effects on Macromolecules Immersed in a Solvent
    渕崎 員弘 JPSJ News Comments 記事・総説・解説・論説等(学術雑誌) 12 13 (2 pages) 2015年12月 [招待有り]
  • 不定形という「形」に魅せられて
    渕崎 員弘 月刊愛媛ジャーナル 記事・総説・解説・論説等(商業誌、新聞、ウェブメディア) 76 -79 2015年04月 [招待有り]
  • 変形Lennard-Jones 系の融解曲線
    渕崎 員弘 愛媛大学理学部紀要 速報,短報,研究ノート等(大学,研究機関紀要) 20 xv -xviii 2015年
  • Lennard-Jones 系の平衡融点
    渕崎 員弘 愛媛大学理学部紀要 速報,短報,研究ノート等(大学,研究機関紀要) 19 i -x 2014年
  • How can we determine a non-crystalline structure from diffraction data?
    SPring-8 Research Frontiers 2007 機関テクニカルレポート,技術報告書,プレプリント等 72 -73 2008年 [招待有り]
  • Balgac–Kusnesov スキームにおける非線形結合項の役割
    渕崎 員弘 愛媛大学理学部紀要 速報,短報,研究ノート等(大学,研究機関紀要) 11 81 -84 2005年
  • Three Topics on Glassy Dynamics in Condensed Matter
    渕崎 員弘 Journal of Rerearch Institute for Science and Technology 会議報告等 9 1 -10 1997年
  • 結晶粒界の幾何学と粒界エネルギー面のフラクタル性
    渕崎 員弘 IIAS Reports 講演資料等(セミナー,チュートリアル,講習,講義他) 85 -91 1997年
  • N. Hamaya, K. Sato, K. Usui, K. Fuchizaki, Y. Fujii, Y. Ohishi ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 研究発表ペーパー・要旨(国際会議) 52 C527 -C527 1996年
  • Structure of Martensific Phase and Phonon Instability in Cu61Zn39
    A. Konishi, Y. Kuroiwa, Y. Noda, K. Fuchizaki, S. Funahashi, S. Katano, H. R. Child, H. Chou, Y. Yamada, S. C. Moss Proceedings of the Fifth International Symposium on Advanced Nuclear Energy Research JAERI-M 93 (228) 468 -474 1993年

共同研究・競争的資金等の研究課題

  • 液ー液転移出現可能性に対する熱力学指標の提案
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 渕崎 員弘
  • 液-液転移理論へのフィードバックを目指した微視的メカニズムの解明
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 渕崎 員弘
     
    液-液転移の微視的過程を明らかにすることが本研究の目的である。平成30年度は二つの大きな成果が得られた。 まず一つ目の成果は液-液クロスオーバを起こすヨウ化ゲルマニウム液体の構造因子の逆モンテカルロ(RMC)解析から得られた。エネルギー分散法によるX線散乱強度から構築した構造因子のRMC解析結果は、加圧とともに分子対称性がTdからC3vに落ちることを示唆した。そこで、これらの対称性を有する場合の分子形状因子を解析的に求めたところ、構造因子の振動の様子の変化を定量的に説明できることが分かった。ヨウ化錫液体も転移の前後で同様な低対称性化を生じている。この分子低対称化を仮定すると、分子間相互作用が二つの特徴長さを持ち得ること、即ち、低密度液体と高密度液体が現れることが自然に示せる。そこで、分子低対称性化は液-液転移の前駆現象であると考えている。 二つ目の成果は分子動力学シミュレーションから得られた。分子性液体は液-液転移を経て高分子化を起こし、高密度化を達成すると考えられているが、実際の微視的過程は観測されていない。そこで、液体ヨウ化ゲルマニウム構造の圧力変化を融解曲線に沿って観察した。約1 GPaまでの圧力範囲で適用可能な模型を用いた。分子間のヨウ素が金属結合化する距離3.6 Å内に接近した際に物理的に「結合」したと見なす。この「結合」は0.1 ps程度の寿命をもつ。この「結合」の浸透確率とクラスターサイズの有限サイズスケーリング解析により、0.85±0.01 GPaで浸透転移が起こることを見出した。ただし、四面体分子の辺-辺配向時の「結合」が主に浸透に寄与する。浸透転移点がヨウ化ゲルマニウムの予想準安定液-液境界の延長線上に位置することは偶然でないと考えている。即ち、ヨウ化ゲルマニウム液体の高密度化は分子間ヨウ素間「結合」の浸透転移によって達成される。
  • ヨウ化物による第二臨界現象発現の立証
    日本学術振興会:科研費 基盤研究(C)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 渕崎 員弘
     
    水のポリアモルフィズムは臨界点シナリオによって矛盾なく、且つ簡潔に説明できる。ただし、その足場となる臨界点はおろか、その付近の低密度水と高密度水そのものを直接観察することは許されない。そこで、代替物質としてヨウ化錫に着目し、「前人未踏」の第二臨界点存在の立証を試みることがが本研究全体の目的である。目的達成に必要な重要な知見が得られた年度であった。 1 GPa付近での圧力領域でのX線小角散乱測定を計画していたが、装置上の制約のため、単色X線吸収測定に変更した。比較的低圧で液体ヨウ化錫を長時間封入保持するために容器蓋の再設計と改良に取り組んだ。これまで実績を積んできたSPring-8 BL22XUでの測定だけではなく、東北大・鈴木昭夫氏のご尽力により、KEK-AR NE7Aを利用した測定も可能になった。KEK放射光X線の横発散の大きさのため、密度に関する定量的な解析は困難なものの、定性的な再現性の確認を行うことができた。 まず、特筆すべき点として、950 Kと1000 Kに保ったまま、圧力印加を行うと、(報告者による理論予想通り)1.5 GPa付近で急な吸収増加が見出される。以前、970 KにてSPring-8で同様な測定を行った際に見出した現象を完全に再現した。これは低密度液相から高密度液相への不連続相転移境界を横切ったことを表している。一方、1200 Kでの圧力印加では、こうした吸収の「跳び」は見られず、単調に吸収が増加する。これらのことより、第二臨界点は間違いなく1.5 GPa付近、1000 Kと1200 Kの間に存在することが言えた。この結果は、この付近での液体構造の局所変化のその場観察の結果と併せてStatPhys26で報告するとともに学術誌に速報する予定である。 また、水に見られるような密度極大が1 GPa未満の低圧領域に現れることも明らかにした。
  • 水型液相間転移の第二臨界点近傍での液体の構造的特徴
    文部科学省:新学術領域研究
    研究期間 : 2011年04月 -2013年03月 
    代表者 : 渕崎 員弘
     
    ヨウ化錫の二液相状態に関して、高圧下での放射光X線その場観察によって、これまで報告者らが得た知見が液相間(第二臨界点)シナリオで矛盾なく、半定量的に説明ができることを示した。ただし、シナリオの完成には液相間に不連続な転移がある実験的証拠を見出す必要があるが、平成23年度までに行った放射光X線吸収によるヨウ化錫液体の密度測定の結果、ほぼそれを手中に射止めている。平成24年度内に論文発表する予定である。水系と異なり、第二臨界点付近の温度・圧力には比較的容易にアクセスすることができることになる。人類初の第二臨界現象の定量的な観察が行えそうである。
  • ヨウ化錫液相-液相間転移のシナリオ
    日本学術振興会:科研費 基盤研究(C)
    研究期間 : 2010年04月 -2013年03月 
    代表者 : 渕崎 員弘
     
    ヨウ化錫液体において観測された二液体を熱力学的に安定な二液相と見なし、これら二液相間転移のシナリオを記述するべく始まった本研究は、この研究期間において 1)当該二液相が確かに熱力学的に安定な相であることを実験的に示したのみならず、2)これら二液相を含めたヨウ化錫系のポリアモルフィズムが水系、および水型の四面体型オープンネットワーク構造をもつ物質のポリアモルフィズムに同形であることを理論的に示した。後者により、水系では到達し得ない、液相-液相臨界点近傍の研究に新たな道を切り開いたことになる。
  • 圧力誘起非晶質化から再結晶化に至るまでの統一的シナリオ
    日本学術振興会:科研費 基盤研究(C)
    研究期間 : 2004年04月 -2006年03月 
    代表者 : 渕崎 員弘
     
    圧力誘起による低対称結晶相→非晶質状態→高対称結晶相への一連の構造の変化を,このような一連の変化を起こす分子性結晶ヨウ化錫を具体例としてとりあげて,これをモデル化することを試みた.ヨウ化錫結晶はヨウ素原子をホストとする格子に錫原子が四面体侵入位置を占めて構築されると考えると後者の侵入に関して局所的規則を得ることができる.これは有限個の手続きで構成され,錫原子を格子ガスとみなした格子ガス模型のハミルトニアンを書き下すことができた.現実の構造はこのハミルトニアンから得られる自由エネルギーを極小にする解として現れる.このようにして「可変構成要素間の熱力学的最適配置」という概念が,圧力誘起による一連の構造変化を統一的に記述する上で有効であることを説くことができた.この考え方に従うと,相転移の途上にある非晶質状態は系のエネルギー-エントロピーの利得による物理的な「帰結」として現れるのである. この考え方は液体状態にも適用でき,圧力誘起によるヨウ化錫液体の液相-液相間相転移の存在を予想した.そこで学際的共同実験プロジェクトを立ち上げ,低圧結晶相の融解曲線が約1.5GPaの圧力を境にその傾きが大きく変化することをまず見出した.即ち,この圧力を境に異なる密度の液体が存在することを意味している.放射光を用いた高温・高圧その場X線観察によって,この圧力付近を境に液体構造が変化することを直接確認することに成功した.これは「可変構成要素間の熱力学的最適配置」なる概念の有効性を実験的に立証したにとどまらず,一般化合物について熱力学的に安定な非晶質状態の多形の存在を初めて明らかにしたという意味で極めて意義がある.「可変構成要素間の熱力学的最適配置」は,正則溶体近似のレベルでは解析的に議論することが可能であり,準安定状態をも含めたヨウ化錫系の圧力-温度相図を推定した.この相図の検証については今年度以降の課題としたい.
  • Statistical-mechanical approach to liquid and amorphous states
    研究期間 : 2005年
  • トポロジカルフラストレーションに起因するスローダイナミクス
    日本学術振興会:科研費 基盤研究(C)
    研究期間 : 2001年04月 -2004年03月 
    代表者 : 渕崎 員弘
     
    トポロジカルフラストレーションとは、系の構成要素、例えば分子、を空間的に充填した際に最適な局所的配置と大域的配置の間に不一致が見られる状況を指し示す。研究代表者はこの状況がガラス等の非晶質構造の構造安定化を担っていると考えた。自由エネルギーコストから考えると、系はフラストレーションの結果生じる「位相欠陥」を出来るだけ空間的に凝縮しようとするであろう。本研究は、正四面体が3次元空間を充填出来ないことに着目し、剛体正四面体からなる理想的な系内にトポロジカルフラストレーションによって生じる位相欠陥を動的密度汎関数法で浮き彫りにし、この位相欠陥の再配置に伴うスローダイナミクスの存在を明らかにしようとするものである。 実際の研究対象としては正四面体対称性を有する分子SnI_4から成る分子性固体を選んだ。このヨウ化錫は圧力誘起により非晶質化することが知られているからである。この非晶質化現象をトポロジカルフラストレーションの立場から議論するのが狙いであった。方法としては分子動力学法による計算機シミュレーションの他、SPring-8での放射光X線による回折実験も行った。これは高圧下での実験的知見に乏しかったからである。一連の研究の結果、非晶質化の直接的原因はフラストレーションによるものではなく、分子解離によるものであることが明らかになった。この事実をもとに、系の構成単位を分子より更に細かい要素に分けるとその新たな構成要素間での最適配置を見出すのがトリビアルな問題ではないことに気づいた。無矛盾な最適配置には更に細かい構成単位が必要となる。即ち、最適配置という観点からは分子解離は物の「理」として理解されるのである。そこで本研究を発展させた新たな課題としてこのことを定量的に明らかにして行く予定である。
  • 結晶粒界の幾何学と粒界エネルギー面のフラクタル性
    日本学術振興会:科研費 基盤研究(C)
    研究期間 : 1996年04月 -1998年03月 
    代表者 : 渕崎 員弘
     
    結晶粒界エネルギーを議論するにあたって粒界で織りなされる様々な格子パターンに内在する幾何学的階層性を数学的に浮き彫りにする新たな方法を案出したわけであるが、この方法に威力を内外に知らしめることが本申請の重要な目的の一つであった。幸運にも本研究は、今年7月米国ピッツバーグにて開催されるこの分野での最高の舞台での一つである「第3回結晶粒成長に関する国際会議」(Third International Conference on Grain Growth)での口頭発表に選ばれた。 さて、平成8年度は方法論の基礎固めとして分子動力学法の整備を行った。粒界エネルギーの結晶粒間のミスオリエンテーション角度依存性を2次元の結晶粒成長モデルに適用した際、定常成長過程に向かう緩和過程が「引き延ばされる」ことを見出したため、当初の計画とは少々異なる方向に研究が進むことになった。この特異な緩和過程はガラスでしばしば見られる緩和過程であり、結晶粒成長で見出された「引き延ばされた」指数緩和を理解するために、ガラスの緩和過程の問題に着手した。ガラスに見られるこのような「遅いダイナミクス」は、一般に様々な緩和プロセスが並列ではなく直列に階層性を成している結果であると理解されている。非常におもしろいことに結晶粒成長で見られた遅い緩和も結晶粒サイズという「メトリカル」な量の緩和過程と結晶粒の角数という「トポロジカル」な量の緩和過程との間に階層構造があることに起因している点を明らかにした。しかるに、その機構の満足な理解にはまだまだこれからの研究に負うところが大きい。またごく最近、高温で平衡状態にある結晶粒界をクエンチすることによって低エネルギー粒界は結晶化をおこすが、高エネルギー粒界が'confined amorphous'状態になることが報告されている。結晶粒界でのガラス転移に付随する熱力学的及び動的性質をバルクのそれと比較研究していくことは今後の興味ある課題であるといえよう。
  • 3次元セルパターンのダイナミクスと幾何学的特徴
    日本学術振興会:科研費 奨励研究(A)
    研究期間 : 1995年04月 -1996年03月 
    代表者 : 渕崎 員弘
     
    一昨年度、3次元セル構造の動力学を記述するためのバ-テックスモデルを案出した。今年度はこのモデルの大規模な計算機シミュレーションを行いセル構造を幾何学的に特徴づける様々な統計量に関するextensiveな解析を行った。その過程で他のモデルに比べて圧倒的な効率の良さで同程度の統計精度を持つ結果が得られることが分かった。また金属或いはセラミックスの多結晶体について実験的に得られているこれら幾何学的統計量の分布も良く再現している。得られた結果の内、特に今後統計力学において理論的な発展を刺激すると考えられる次の2点に関して述べる。 1.ボロノイセルパターンからのずれとセルの体積分布関数(結晶粒成長国際会議招待講演) ボロノイセルによる空間のランダム分割に関しては幾つかの厳密な結果が知られており、これを成長するセル構造にも適応する試みがあるが、背後にある物理を無視し得ないことが得られたセルの面数分布からも明らかになった。また一方ではランダムボロノイ分割によるセルの体積分布はΓ-分布で特徴づけられる事が分かっているがこの事とシミュレーションの結果は矛盾しない。即ち、背後にあるセルの成長機構によりΓ-分布の特殊な場合である指数分布が実現していると考えられる。 2.3次元セルパターンにおけるvon Neumann則(StatPhys-Taipei-1995招待講演) 2次元セル構造系からの類推で3次元セル構造においてもセルの平均成長率はその面数のリニアな関数であると予想されていたが現時点での我々のシミュレーションで得られた結果から判断する限りこの予想は正しくないことが分かった。但しこの点については現モデルを更に改良して今後も検討して行く予定である。
  • 固体におけるセル構造のダイナミクス
    日本学術振興会:科研費 奨励研究(A)
    研究期間 : 1993年04月 -1994年03月 
    代表者 : 渕崎 員弘
     
    固体中での結晶粒成長のダイナミクスを議論するための計算機シュミレーションプログラムを開発しこれを実行した。2次元セル構造の計算機シュミレーションは今日では充分行われている。併せて理論的な統計力学的取扱いもなされている。しかしながら理想的な2次元系をつくる事は実際的には困難であり、実験との比較を行うための3次元系の効率的なシュミレーションの方法の開発が望まれていた。既にポッツモデルによるモンテカルロシュミレーションは行われているがそのコストパフォーマンスは著しく悪いだけでなく、物理的な時間空間スケールが決まらないという原理的な困難を抱えていた。そこでセル構造の自由度をセルの頂点の自由度にまで縮約したモデル「バ-テックスモデル」に基づくシュミレーション方法を開発した。即ち、セル壁(界面)を三角形分割し界面の運動方程式より各三角形頂点の運動方程式を導き、これを時間方向に積分する事で各頂点、即ち、セル形状の時間発展を追跡する事が出来る。空間時間的な粗視化の目安となるカットオフ長以下でのイベントはトポロジーの変化(セル間でのスイッチング及びセルの合体)として処理した。この様にしてポッツモデルによる方法での困難をすべて克服する事が出来た。シュミレーションの結果、面数分布及びセルサイズ分布に関してはポッツモデルによる大規模シュミレーションで得られた結果をカバーしただけでなく、今回新たにAboav-Weaire則及びLewis則が3次元セル系でも成立する事を高精度で確認した。後者はセル構造による空間充填という純粋に幾何学的な要請によるものと考えられる。これらの結果は2編の論文にて出版する予定である。 これと並行してフラストレートした氷のモデルを統計力学的に論じた。このモデルは界面上での新しいタイプの相転移として今後発展させる予定である。
  • Relaxation processes in supercooled liquids
    研究期間 : 1987年
  • Geometrical Aspect of Grain Boundaries
  • Dynamics of Cellular Patterns

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