Shoji Kashida

X-ray study of the average structures of Cu2Se and Cu1.8S in the room temperature and the high temperature phases

Abstract The structures of the antifluorite-type copper chalcogenides Cu 2 Se and Cu 1.8 S were studied using single crystal X-ray diffraction data both below and above the transition point. Using the cubic indexing main reflections, the average structures of the compounds were refined by least...

X-ray study of the incommensurate phase of

The successive structural phase transitions in the layer compound have been studied using single-crystal x-ray diffraction. The intermediate phase between 194 K and 214 K is found to be incommensurate; the satellite maps show that the modulation mode which characterizes the intermediate phase has . It is shown that the previously reported satellite reflections at are ascribable to twins. A structure model is presented for the incommensurate phase. In the low-temperature phase below 197 K, the satellite reflections are shifted to a commensurate position, .

Structural phase transition in KHCO3

Abstract The structural phase transition of KHCO 3 has been studied using three-dimensional data collected both below and above the transition point. Above 318 K, the crystal structure changes from the room temperature phase (monoclinic space group P2 1 a ) to a high temperature phase (monoclinic space group C2 m ), both containing four formula units. The cell dimensions are a = 15.195(1) A, b = 5.640(1) A, c = 3.734(1) A, and β = 104.86(1)°, and v = 309.28 A 3 (at 353 K). The structure is refined by the full-matrix least-squares method and final R -factor is 0.023. From the hydrogen atoms revealed in the difference Fourier map, it is concluded that the phase transition is ascribed to the order-disorder of the (HCO 3 ) 2 dimer.

X-ray study of the cation distribution in Cu2Se, Cu1.8Se and Cu1.8S; analysis by the maximum entropy method☆

Abstract The structures of fast ion conductors Cu2Se, Cu1.8Se and Cu1.8S have been studied with the use of single crystal X-ray diffraction data. The compounds have cubic antifluorite structures, copper ions and distributed to the tetrahedral, trigonal and octahedral interstitials of the chalcogen atoms. In the refinement of the structures, the maximum entropy method (MEM) is used to construct the density map of the copper ions. The distribution of the copper ions is studied as a function of temperature. The diffusion path of the mobile copper ions is also discussed. The present method, MEM is found to have several advantages over the previous methods, such as the split atom, the anharmonic and the excluded volume models.

Ultrasonic Velocities in BaTiO3

The sound velocities in BaTiO 3 has been observed near its paraelectric to ferroelectric phase transition point. The anomalous part of the sound velocity of the longitudinal wave propagating along [100] direction depends on temperature as A [( T - T 0 )/ T 0 ] -ζ with ζ=0.41 and A =1.79×10 4 cm·sec -1 where T 0 is the paraelectric temperature. The critical index ζ is close to the theoretical value of 1/2 as predicted by Dvořak. On the other hand, the velocity of the transverse wave does not show any appreciable critical behavior. The value of A is also compared with the theory given by Dvořak. The observed curve for the longitudinal wave is in good agreement with the theoretical curve, while that for the transverse wave shows a notable discrepancy.

Electronic structure of Ag2Te, band calculation and photoelectron spectroscopy

Abstract The electronic structure of Ag 2 Te has been investigated, theoretically using the self-consistent full-potential linear-muffin-tin-orbital (LMTO) calculation, and experimentally using photoelectron spectroscopy. Comparison of the calculated and measured photoemission data shows, in general, good agreement. Based on the total energy calculations performed for several model structures, the stability of the tetrahedral and octahedral Ag coordinations is examined. It is found that the α–β phase transition is ascribed to the energy lowering accompanying the Ag coordination change and the atomic displacements in the β-Ag 2 Te. The fast-ionic diffusion paths of Ag atoms in the high temperature phase are also discussed.

Inelastic Neutron Scattering Study of KHCO3

The incoherent inelastic neutron scattering study in a KHCO 3 single crystal is reported. KHCO 3 crystal contains (HCO 3 ) 2 dimers linked by hydrogen-bonds. Neutron scattering experiments were done in order to study the hydrogen motions in the dimer. Two OH bending modes were detected, with polarizations one in the dimer plane and the other out of this plane. The obtained results were analyzed by comparing with recent infrared, Raman and powder neutron scattering data. The angular dependence of the neutron scattering spectra was found to be very useful to identify the hydrogen modes in crystalline states.

An X-ray study of the incommensurate structure in digenite (Cu1.8S)

The structure of a non-stoichiometric copper compound Cu1.8S (digenite) has been studied by X-ray diffraction. Although digenite has a cubic anti-fluorite structure, satellite reflections were seen along the (111)c axis. Single-crystal X-ray diffraction data, including first- and second-order satellites, were collected using a four-circle diffractometer. A rhombohedral twinning model was used to determine the modulation densities of the copper ions. The final R-factor is about 10% including the main and satellite reflections. The present analysis shows that the crystal is composed of domain-like structures: in each domain, the dimensions of the regular lattice, formed from copper ions, are slightly larger than those of the basic sulphur lattice. The origin of this domain-like structure, based on the Frenkel-Kontorova model, is attributed to the non-stoichiometry and apparently smaller cation-anion interaction.

p–d hybridization in superionic conductors

Abstract The band calculations of AgX (X=halogen), CuX (X=halogen) and β-Ag 3 SX (X=I, Br) are studied to reveal the high ionic conductivity of Ag + and Cu + in these superionic conductors using the linear combination of atomic orbitals (LCAO) theory. It is found that the d states of Ag + are much more weakly coupled with the p states of halogen ions, while those of Cu + are much more strongly coupled with the p bands. The strength of p – d hybridization is discussed to connect with the activation energy for the ionic conduction. It is shown that the high ionic conductivity of AgX (X=halogen) and β-Ag 3 SX (X=I, Br) primarily stems from the combination of the deformability of d shell and the weakness of p – d hybridization.

Ferroelectric phase transition in monoclinic TlS

Abstract The dielectric property of newly found monoclinic thallium monosulfide (TlS) has been investigated in the temperature range from 285 to 380 K. The dielectric constants show anomalous increases at 3186 and 341.1 K suggesting the occurrence of successive phase transitions. A study of the polarization hysteresis loop shows that this compound is ferroelectric in the room temperature phase. The nature of the phase transitions is probed by calorimetric and X-ray measurements.