title: Variable-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type barium titanate phases.
abstract: A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3 perovskite has been performed over the temperature range 298-778 K. A transition from a tetragonal (P4mm) to a cubic (Pm3m) phase has been revealed near 413 K. In the non-centrosymmetric P4mm symmetry group, both Ti and O atoms are displaced along the c-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti(4+) and Ba(2+) cations occupy off-center positions in the TiO6 and BaO12 polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.
authors.affiliation: Graduate School of Sciences and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
authors.forename: Tomotaka
authors.initials: T
authors.lastname: Nakatani
authors.affiliation: Graduate School of Sciences and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yoshiasa
authors.affiliation: Graduate School of Science and Engineering, Yamaguchi University, Ube, Yamaguchi 755-8611, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nakatsuka
authors.affiliation: Graduate School of Sciences and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hiratoko
authors.affiliation: Graduate School of Sciences and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Mashimo
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-850, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Okube
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-850, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sasaki
mesh_terms: D001464:Barium / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D015394:Molecular Structure; D010087:Oxides / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D017610:Calcium Compounds; D002412:Cations; D010087:Oxides; C059910:perovskite; D001464:Barium; D014025:Titanium
keywords: BaTiO3; X-ray diffraction; ferroelectricity; high temperature; perovskite