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Defect control for polarization switching in BiFeO<sub>3</sub> single crystals
Chishima, Yuji,Noguchi, Yuji,Kitanaka, Yuuki,Miyayama, Masaru IEEE 2010 and Frequency Control Vol.57 No.10
<P>BiFeO<SUB>3</SUB> (BFO) single crystals were grown and the effects of Zn and Mn co-doping on the polarization and leakage current properties were investigated at 25°C for establishing materials design based on defect chemistry. Although Zn doping or Mn doping led to a deterioration in the properties, Zn-Mn co-doping led to a large remanent polarization (36 μC/cm<SUP>2</SUP>), a low coercive field (19 kV/cm), and a relatively low leakage current density (~10<SUP>-8</SUP> A/cm<SUP>2</SUP>). It is proposed that defect dipoles composed of Zn<SUP>2+</SUP> and Mn<SUP>4+</SUP> act as effective nucleation sites for ferroelectric domains during polarization switching in BFO crystals.</P>
Crystal Structure and Polarization Properties of Ferroelectric Bi4−xLaxTi3O12 Single Crystals
Masaru Miyayama,Yuji Noguchi,Masayuki Soga 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
Single crystals of ferroelectric Bi4Ti3O12 (BiT) and La-substituted Bi4Ti3O12 (BLT) were grown by using a self-flux method, and the effects of La substitution on the crystal structure, the polarization properties, and the domain structure were investigated. BLT crystals showed a smaller remanent polarization along the a axis compared with BiT, which is in good qualitative agreement with the spontaneous polarization calculated from the structural data determined from the neutron diffraction analysis. La substitution resulted in a decrease in the domain width of 90 degree domains, which is attributed in part to the smaller structural distortion a/b for BLT. Single crystals of ferroelectric Bi4Ti3O12 (BiT) and La-substituted Bi4Ti3O12 (BLT) were grown by using a self-flux method, and the effects of La substitution on the crystal structure, the polarization properties, and the domain structure were investigated. BLT crystals showed a smaller remanent polarization along the a axis compared with BiT, which is in good qualitative agreement with the spontaneous polarization calculated from the structural data determined from the neutron diffraction analysis. La substitution resulted in a decrease in the domain width of 90 degree domains, which is attributed in part to the smaller structural distortion a/b for BLT.
Electrical conduction properties of La-substituted bismuth titanate single crystals
Masaru Miyayama,Yuji Noguchi,Masatake Takahashi 한양대학교 세라믹연구소 2005 Journal of Ceramic Processing Research Vol.6 No.4
Single crystals of lanthanum-substituted bismuth titanate were grown by a self-flux method, and electrical conductivities were investigated at high temperatures. Lanthanum substitution suppressed Bi vaporization during annealing and decreased the electrical conductivity in both the a- and c-axes. It is suggested that lanthanum substitution stabilizes the perovskite blocks and hence decreases the concentrations of oxygen vacancies and holes as the conduction carriers. An ab-initio calculation indicated that the formation energy of an oxygen vacancy in the perovskite block is increased by lanthanum substitution, supporting the above experimental results.
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.
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.
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.