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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.
A New Method for Evaluating the Electrostatic Potential by Using a MEM X-Ray Diffraction Analysis
Hiroshi Tanaka,Yoshihiro Kuroiwa,Masaki Takata 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
Recently, a new method was proposed for evaluating the electrostatic potential in crystalline solids from X-ray diffraction data. It is based on the electron charge density, which is analyzed by using the maximum entropy method (MEM) and Ewald's technique. The algorithm is almost parameter-free, and the electrostatic potential can be evaluated even by those with little or no experience. In this article, the method is reviewed briefly, and an application to a typical ionic crystal, NaCl, is introduced. Recently, a new method was proposed for evaluating the electrostatic potential in crystalline solids from X-ray diffraction data. It is based on the electron charge density, which is analyzed by using the maximum entropy method (MEM) and Ewald's technique. The algorithm is almost parameter-free, and the electrostatic potential can be evaluated even by those with little or no experience. In this article, the method is reviewed briefly, and an application to a typical ionic crystal, NaCl, is introduced.
An electrostatic potential study of asymmetric ionic conductivity in Li_2B_4O_7 crystals
김수재,김원경,조용찬,박성균,정일경,양용석,Yoshihiro Kuroiwa,Chikako Moriyoshi,Hiroshi Tanaka,Masaki Takata,정세영 한국물리학회 2011 Current Applied Physics Vol.11 No.3
This study investigated the bonding nature and electrostatic potential of asymmetric Li ionic mobility in Li_2B_4O_7 crystals using the maximum entropy method (MEM) combined with Rietveld refinement and Ewald’s technique. Compared with the interaction between oxygen and boron, Li^+ ions exhibited weak interactions with both oxygen and boron. Furthermore, electrostatic-potential-distribution analysis showed that Li^+ ions had a much weaker interaction with the matrix along the c-axis channel, suggesting that higher ionic conductivity occurred along the c-axis than along the a- and b-axes.
Atomic Replacement Eect on Electron Charge Density of Perovskite Oxides
Yoshihiro Kuroiwa,Shinobu Aoyagiy,Akikatsu Sawada,Eiji Nishibori,Masaki Takata,Makoto Sakata,Hiroshi Tanaka,Jimpei Harada 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Charge density distributions of cubic SrTiO3 have been investigated related to the atomic replacement eect on the phase transition, by analyzing the synchrotron-radiation X-ray powder-diraction data by the MEM(Maximum Entropy Method)/Rietveld method. The chemical bonding natures between constituent atoms in cubic SrTiO3 are compared with those in cubic BaTiO3 that we investigated previously at the same temperature. The Characteristic charge density distribution around the O atom, which may present a clue what kind of phase transition occurs in the cubic perovskite oxide, is found in SrTiO3.
Atomic Replacement Effect on Electron Charge Density of Perovskite Oxides
Yoshihiro Kuroiwa,Akikatsu Sawada,Eiji Nishibori,Hiroshi Tanaka,Jimpei Harada,Makoto Sakata,Masaki Takata,Shinobu Aoyagi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Charge density distributions of cubic SrTiO3 have been investigated related to the atomic replacement eect on the phase transition, by analyzing the synchrotron-radiation X-ray powder-diraction data by the MEM(Maximum Entropy Method)/Rietveld method. The chemical bonding natures between constituent atoms in cubic SrTiO3 are compared with those in cubic BaTiO3 that we investigated previously at the same temperature. The Characteristic charge density distribution around the O atom, which may present a clue what kind of phase transition occurs in the cubic perovskite oxide, is found in SrTiO3.