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Core/Shell Structure of Ferroelectric (Ba0.94Ca0.06)TiO3 Grains
Yoshihiro Iwahori,Hiroshi Tanaka,Masaki Takata,Yoshihiro Terado,Chikako Moriyoshi,Yoshihiro Kuroiwa 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
The crystal structure of ferroelectric (Ba0.94Ca0.06)TiO3 (BCT) with small grains on an average of 1-μm in size has been investigated by using high-energy synchrotron-radiation powder-diffraction. A core/shell structure model, in which the grain consists of a core with tetragonal symmetry covered all over with a thin tetragonal shell with low tetragonality, is proposed and provides a markedly contrast with the core/shell structure of pure BaTiO3, which is generally known to have a shell with cubic symmetry. The higher permittivity of BCT is attributed to the characteristic shell structure with tetragonal symmetry. A change in the chemical bonding nature of BCT on the ferroelectric phase transition is clearly demonstrated in the electron charge density map. The crystal structure of ferroelectric (Ba0.94Ca0.06)TiO3 (BCT) with small grains on an average of 1-μm in size has been investigated by using high-energy synchrotron-radiation powder-diffraction. A core/shell structure model, in which the grain consists of a core with tetragonal symmetry covered all over with a thin tetragonal shell with low tetragonality, is proposed and provides a markedly contrast with the core/shell structure of pure BaTiO3, which is generally known to have a shell with cubic symmetry. The higher permittivity of BCT is attributed to the characteristic shell structure with tetragonal symmetry. A change in the chemical bonding nature of BCT on the ferroelectric phase transition is clearly demonstrated in the electron charge density map.
Charge Density Distribution of PbHfO3 in Antiferroelectric Phase
Yoshihiro Terado,Yoshihiro Kuroiwa,Chikako Moriyoshi,Hitoshi Kawaji,Tooru Atake 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Electron charge density distributions of PbHfO3 in the antiferroelectric phase with an orthorhombic structure have been revealed by analyzing the high-energy synchrotron-radiation powder diffraction data using the maximum entropy method/Rietveld method. The covalent bonding natures of both the Pb-O and Hf-O bonds are clearly visualized at 100 K. The formation of Pb-O electron orbital hybridization is a new finding which characterizes the antiferroelectric phase, whereas Pb is ionic in the paraelectric phase with a cubic structure.