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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.
Raman Scattering Study of Antiferroelectric Phase Transition in Cu(HCOO)2-4H2O
Takuya Mizushima,Akira Sakai,Chikako Moriyoshi,Kazuyuki Itoh,Takeru Omura 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Micro-Raman scattering spectra of copper formate tetrahydrate, Cu(HCOO)24H2O, were observed above and below the antiferroelectric phase transition temperature with special attention to internal modes of HCOO and H2O molecules. In the antiferroelectric phase, the symmetric stretching vibration in HCOO at 1375 cm1 splits into two modes and the degree of splitting increases with decreasing temperature. The splitting is caused by doubling of the unit cell, rather than inequivalence of the molecular site due to the reduction in symmetry. Two Ag spectra observed in b(aa)b and a(cc)a geometries show the different temperature dependence in the frequency regions of H2O symmetric stretching and C-H symmetric stretching vibrations. The dierence is discussed in terms of the two-dimensional arrangement of H2O layers in the crystal.
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.
Ken Yanai,Hiroaki Onozuka,Yuuki Kitanaka,Yuji Noguchi,Masaru Miyayama,Chikako Moriyoshi,Yoshihiro Kuroiwa,Kousuke Kurushima,Shigeo Mori 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
Single crystals of ferroelectric (Bi<SUB>0.5</SUB>Na<SUB>0.5</SUB>)TiO<SUB>3</SUB> were successfully grown by the top-seeded solution growth method at a high oxygen pressure of 0.9쟋Pa and their polarization switching dynamics along <100><SUB>c</SUB> and their domain structures were investigated. Piezoelectric force microscope (PFM) observations show that BNT crystals poled along <100><SUB>c</SUB>. had 71-degree domains in which the spontaneous polarization (<I>P</I><SUB>s</SUB>) vector is opposite to the poling electric fields. Synchrotronradiation single-crystal X-ray diffraction analyses and the PFM observations reveal that the polarization switching in the BNT crystals along <100><SUB>c</SUB> is achieved by a 71-degree rotation of the <I>P</I><SUB>s</SUB> vector.
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.
Park, Ji Hun,Lee, Yeong Ju,Bae, Jong-Seong,Kim, Bum-Su,Cho, Yong Chan,Moriyoshi, Chikako,Kuroiwa, Yoshihiro,Lee, Seunghun,Jeong, Se-Young Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1
<P>Oxygen vacancy (V<SUB>O</SUB>) strongly affects the properties of oxides. In this study, we used X-ray diffraction (XRD) to study changes in the V<SUB>O</SUB> concentration as a function of the Co-doping level of ZnO. Rietveld refinement yielded a different result from that determined via X-ray photoelectron spectroscopy (XPS), but additional maximum entropy method (MEM) analysis led it to compensate for the difference. V<SUB>O</SUB> tended to gradually decrease with increased Co doping, and ferromagnetic behavior was not observed regardless of the Co-doping concentration. MEM analysis demonstrated that reliable information related to the defects in the ZnO-based system can be obtained using X-ray diffraction alone.</P>