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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.
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.
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.
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.
Disorder in the Cubic Phase of PbHfO3 by High Energy Synchrotron Radiation Diffraction
Yoshihiro Kuroiwa,Akikatsu Sawada,Hiroshi Fujiwara,Hitoshi Kawaji,Tooru Atake 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The electron charge density distributions of PbHfO3 in the cubic phase have been investigated in association with the antiferroelectric phase transition, by analyzing high-energy synchrotronradiation powder diraction data by the maximum entropy method (MEM)/Rietveld method. The Pb atom is found to be ionic and disordered in the h100i direction. Clear covalency is observed on the Hf-O bonding. The charge density distributions around the O atom are extremely anisotropic, and are extended in the directions perpendicular to the Hf-O covalent bond. These structural characteristics are observed both at 500 K near Tc (= 476 K) and at 700 K far above Tc.
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.
Charge Density Study of Negative-Thermal-Expansion Material ZrW2O8
Ayumi Kojima,Yoshihiro Kuroiwa,Akikatsu Sawada,Noriyuki Nakajima,Shinobu Aoyagi,Toshihide Tsuji,Yasuhisa Yamamura 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
The covalent bonding nature of the negative thermal expansion material, ZrW2O8, has been revealed in the accurate charge-density distribution at 300 K, by analyzing the synchrotron-radiation high-energy powder-diraction data by the MEM/Rietveld method. It is found that two WO4 tetrahedra are bonded covalently by the bridging O atom along the body diagonal directions in the cubic structure. The bonding electron density between the W atom and the terminal O atom, which has a key to the mechanism of the order-disorder phase transition, is highest among the W-O covalent bonds.
Charge Density Distributions in Bi4Ti3O12 and Bi3.25La0.75Ti3O12 in the Paraelectric Phase
Chikako Moriyoshi,Sayaka Kimura,Yoshihiro Kuroiwa,김수재,Yuji Noguchi 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
The electron charge density distributions of the bismuth layered ferroelectric materials Bi4Ti3O12 (BiT) and Bi3.25La0.75Ti3O12 (BLT) in the paraelectric phase are demonstrated by analyzing the high-energy synchrotron-radiation powder-diffraction data on the basis of the maximum entropy method (MEM)/Rietveld method. The crystal structures of BiT and BLT are quite similar, and no significant difference is observed in the chemical bonding nature in the paraelectric phase. This result differs from the experimental fact that, in the ferroelectric phase, electron orbital hybridization between Bi and O in the perovskite layer is formed along the a-axis in BiT while the hybridization between Bi/La and O is revealed not only along the a-axis but also along the b-axis in BLT. We attribute the unchanged Curie temperatures for the Bi4−xLaxTi3O12 system to the same crystal structures, including the chemical bonding nature, in the paraelectric phase. The electron charge density distributions of the bismuth layered ferroelectric materials Bi4Ti3O12 (BiT) and Bi3.25La0.75Ti3O12 (BLT) in the paraelectric phase are demonstrated by analyzing the high-energy synchrotron-radiation powder-diffraction data on the basis of the maximum entropy method (MEM)/Rietveld method. The crystal structures of BiT and BLT are quite similar, and no significant difference is observed in the chemical bonding nature in the paraelectric phase. This result differs from the experimental fact that, in the ferroelectric phase, electron orbital hybridization between Bi and O in the perovskite layer is formed along the a-axis in BiT while the hybridization between Bi/La and O is revealed not only along the a-axis but also along the b-axis in BLT. We attribute the unchanged Curie temperatures for the Bi4−xLaxTi3O12 system to the same crystal structures, including the chemical bonding nature, in the paraelectric phase.
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.
Shotaro Ishikawa,Yuuki Kitanaka,Takeshi Oguchi,Yuji Noguchi,Masaru Miyayama,Chikako Moriyoshi,Yoshihiro Kuroiwa 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
Domain structures and dynamics of BaTiO<SUB>3</SUB> single crystals under in-situ electric fields along <101> were investigated by using synchrotron radiation single-crystal X-ray diffractions. Diffraction patterns clearly show the presence of a 90 o domain structure in crystals poled along <101>. The linear characteristics of strain and polarization with unipolar electric fields along <101> suggested that the 90˚ domain structures established by poling treatments do not change by applying electric fields. The diffraction analysis, however, provides direct evidence of a reversible change in the volume fractions of two kinds of the 90˚ domains under unipolar in-situ electric fields.