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Sakuma, Takashi*; Basar, K.*; Xianglian*; Siagian, S.*; Takahashi, Haruyuki*; Igawa, Naoki
no journal, ,
Diffuse scatterings contain information about a short-range-order and thermal vibrations of atoms in crystals. We discuss the inter-atomic distance and temperature dependence of the correlation effects among thermal displacements of atoms. The intensity of neutron diffuse scattering for silver halides and copper halides was analyzed with the correlation effects among thermal displacements of first, second and third nearest beighboring atoms. the values of the correlation effects decrease rapidly with the increase of inter-atomic distance. Those also decrease with the decrease of temperature and the tendency of the temperature dependence agrees with that obtained by the simple Debye model of lattice vibrations.
Yoneda, Yasuhiro; Kohara, Shinji*
no journal, ,
Local structures of BaTiO
and BiFeO perovskite ferroelectrics were investigated by X-ray pair-distribution function (PDF) analysis in wide temperature ranges. In BaTiO, the high-temperature cubic structure deformed to rhombohedral structure through three phase transitions. On the other hand, in BiFeO the high-temperature cubicstructure deformed to the rhombohedral structure through only one phase transition. The temperature evolution of the PDFs for BaTiO and BiFeO indicated that in BaTiO, the positions of the PDF peaks did not change too much excluding the temperature factor. In BiFeO the shapes of PDF peaks changed drastically at the phase transition temperature. Thus, we found two types of phase transitions in ferroelectrics. In one, the average structure changed, but local structure unchanged like BaTiO. Another is that both average and local structure changed like BiFeO.
Shamoto, Shinichi
no journal, ,
There are modern functional materials with disordered crystal structures. These functional materials have disordered part and high crystalline part in their crystal structures. The atomic pair distribution function (PDF) analysis is suitable to investigate their disordered crystal structures. For example, the importance of the research would be how effectively disorders are introduced in their crystal structures, while keeping the electric conducting part to be highly crystalline. Pulsed neutron powder diffraction is one of the best tools for this type of research.