Kazuhiro Fuchizaki

Preparation and crystal structure of Sr2CuO2(CO3)

Abstract Sr 2 CuO 2 (CO 3 ) was prepared at 1273 K and 0.01 MPa CO 2 partial pressure in a flowing gas of O 2 CO 2 using a mixture of SrCO 3 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) A , and its space group is 14. The formula per unit cell is 8 Sr 2 CuO 2 (CO 3 ), and measured and calculated densities are D m = 4.71 g/cm 3 , and D x = 4.81 g/cm 3 , 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 [CuO 6 ] octahedrons and layers of ordered triangular CO 3 groups. Sr atoms having eight near oxygen neighbors are between the [CuO 6 ] octahedrons and the CO 3 layers.

Computer modelling of three-dimensional cellular pattern growth

Abstract The time evolution of three-dimensional cellular patterns is discussed on the basis of the oertex model which consists of a set of equations for the motion of vertices obtained from the fu...

Phase diagram of the modified Lennard-Jones system

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 ε∕k(B) and 0.0018(5) ε∕σ(3), and those of the critical point were 1.0709(19) ε∕k(B) and 0.1228(20) ε∕σ(3), where ε and σ 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.

Polyamorphism in tin tetraiodide.

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.

Search for precursor of pressure-induced amorphization of molecular crystal SnI4: Thermodynamic stability of low-pressure crystalline phase

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 f...

Dynamical density functional theory for glassy behaviour

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.

Precise Determination of the Melting Point of a Modified Lennard-Jones System

Much progress has been made in understanding superheating phenomena in solids owing to developments in experimental techniques with which to control the surface condition of crystals. However, the ultimate condition determining the thermodynamic instability of solid state is still controversial. Prior to discussing subtle differences in the amount of superheating brought about by the different mechanisms proposed thus far, the equilibrium phasetransition point, i.e., the melting point should be precisely determined. To the best of our knowledge, however, no precise value of the melting point even for a simpler system, such as a Lennard-Jones (LJ) system, has been updated. In this study, we try to determine as precisely as possible the melting point of a LJ system, since most of the numerical works dealing with the superheating phenomena employ the LJ potential. In order to obtain the intrinsic thermodynamic property of the system, the cutoff of the potential tail at a certain distance should be avoided. Then, two approaches are possible; the first one is achieved by mathematically converting the sum of the potential to another form that converges much faster. The other one is to modify the potential form in such a way that it smoothly vanishes at a certain distance, while the most part, except the immediate vicinity of the vanishing point, remains unmodified. Here, we take the latter approach by adopting the modified form, m, employed in ref. 6. The well-established Ar parameters 7)

Communication: probable scenario of the liquid-liquid phase transition of SnI4.

We have shown from in situ synchrotron x-ray diffraction measurements that there are two thermodynamically stable liquid forms of SnI(4), 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.

Synchrotron x-ray studies of molecular liquid SnI4

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.

Orientation effect on grain growth

The effect of crystal orientation of grains on grain growth is investigated by computer simulation. A vertex model which includes the orietation 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 12-power growth law of the average size of grains still holds under such an anisotropic circumstance.