Shuta Tahara

Intermediate-range chemical ordering of cations in molten RbCl-AgCl

A first sharp diffraction peak (FSDP) is observed in the X-ray total structure factor of a molten mixture of RbCl-AgCl, while both pure melts of RbCl and AgCl do not exhibit FSDP individually. Molecular dynamics simulations were performed to investigate the origin of the FSDP with the polarizable ion model (PIM). Coexistence of covalent Ag-Cl and ionic Rb-Cl bonds leads the system to evolve intermediate range ordering, which is simulated by introducing the induced polarization in different ways between Ag-Cl with fully polarizable treatment based on Vashishta-Raman potential and Rb-Cl with suppression over-polarization in the nearest neighbor contribution based on Born-Meyer potential. The partial structure factors for both the Ag-Ag and Rb-Rb correlations, SAgAg(Q) and SRbRb(Q), show a positive contribution to the FSDP, while SAgRb(Q) for the Ag-Rb correlation exhibits a negative contribution, indicating that Ag and Rb ions are distributed in an alternating manner within the intermediate-range length scale. The origin of the intermediate-range chemical ordering of cations can be ascribed to the preferred direction of the dipole moments of anions in the PIM.

Anion Polarization Effects on Static Structure and Ionic Transport in Superionic Melt of RbAg4I5

The anion polarization effects on the static structure and ionic transport in the superionic melt of RbAg4I5 are investigated by molecular dynamics simulations with the rigid ion model and the polarizable ion model (PIM). The first sharp diffraction peak (FSDP) observed in the experimental static structure factor is reproduced in the case of the PIM, and cation–cation partial structure factors show the characteristic FSDP for Ag–Ag and Rb–Rb correlations and a negative FSDP for the Ag–Rb correlation, indicating that Ag and Rb ions are alternately distributed with an intermediate-range length scale. Ag ions form small clusters of the various sizes, which relates to the density fluctuation and intermediate-range ordering of Ag ions. Rb and the surrounding I ions generate the regions where Ag ions cannot penetrate with the radius of 4–5 A, which is revealed by void analysis by the Voronoi–Delaunay method. The superionic feature remains even in the molten state since the diffusion coefficient of Ag ions is se...

Thermal Properties and Structures of CsHSO4and CsDSO4 Crystals

Differential scanning calorimetry, thermogravimetric-differential thermal analysis, and Xray diffraction measurements were performed on cesium hydrogen sulfate (CsHSO 4) and deuterated CsDSO 4 crystals. The proton and deuterated compounds were confirmed to exhibit the superionic phase transition at 415.9 and 413.4 K, respectively. The II-III transition for the proton compound was observed in the temperature range of about 330400 K. The thermal decomposition and dehydration reactions of both compounds began at around 460 K. The decomposition continued up to around 1050 K, and the dehydration ended at around 720 K. The weight losses in the temperature ranges of 460-720 K and 720-1050 K were caused by the evaporation of H(D) 2O and SO 3, respectively. The space group symmetries and structural parameters, in phase III (monoclinic, P21/n) for CsHSO 4 and in phase II (monoclinic, P21/c) for CsHSO 4 and CsDSO 4, were determined at room temperature. The expansion of O-H-O hydrogen bond caused by the substitution of deuterium for hydrogen was observed to be 0.015(4) A. The geometric isotope effect on hydrogen-bond structure upon deuteration was realized in the CsHSO 4 crystal. The difference in morphology between as-grown CsHSO 4 and CsDSO 4 crystals was suggested to be caused by the large expansion of the O-H-O hydrogen bond upon deuteration on crystallization in D 2O aqueous solution.

The structure of molten CuCl: Reverse Monte Carlo modeling with high-energy X-ray diffraction data and molecular dynamics of a polarizable ion model

The results of the structural properties of molten copper chloride are reported from high-energy X-ray diffraction measurements, reverse Monte Carlo modeling method, and molecular dynamics simulations using a polarizable ion model. The simulated X-ray structure factor reproduces all trends observed experimentally, in particular the shoulder at around 1 Å(-1) related to intermediate range ordering, as well as the partial copper-copper correlations from the reverse Monte Carlo modeling, which cannot be reproduced by using a simple rigid ion model. It is shown that the shoulder comes from intermediate range copper-copper correlations caused by the polarized chlorides.

Magnetic Property of Liquid 3d Transition Metal–Al Alloys

Measurements of the magnetic susceptibilities χ of liquid 3d transition metal–Sb alloys were carried out systematically to determine the composition of transition metals where the magnetic-to-nonma...

Fluctuations in medium-range structure of Bi-based metallic liquid alloys

Liquid structure of Bi50Zn50, which is situated at around the Bi-rich end of miscibility gap in Bi-Zn system, has been investigated by neutron and x-ray diffraction experiments and following analysis using reverse Monte Carlo (RMC) structural modelling. Among the partial correlations calculated from the structural model obtained by RMC, the Zn-Zn partial has a large temperature variation. It is found that there are medium-range fluctuations in Zn distribution which have a scale of 10 A.

Transport Properties of Molten CuCl–Cu2Se Mixtures

The electrical conductivity, σ, and the thermoelectric power, S , have been measured for molten CuCl–Cu 2 Se mixtures as a function of composition and temperature. The electrical conductivity of their mixtures decreases rapidly with the addition of CuCl to liquid Cu 2 Se. The thermoelectric power of molten CuCl–Cu 2 Se mixtures shows a steady increase with increasing amount of CuCl. The experimental results suggest that the dominant transport process in the molten CuCl–Cu 2 Se mixtures changes from electronic to ionic conduction. The composition dependence of σ and S was analyzed by using the fundamental equation of electrical current densities due to the electrons and the ions. According to this analysis, the conductivity gap increases gradually upon the addition of CuCl to liquid Cu 2 Se, and the conductivity gap is about 0.68 eV for a molten (CuCl) 0.3 (Cu 2 Se) 0.7 mixture.