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Heat capacity, X-ray scattering and neutron scattering studies in Rb2SeO4
Hirotake Shigematsu,Hiroyuki Mashiyama,Hitoshi Kawaji,Takeo Tojo,Tooru Atake,Yukikuni Akishige 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The structural phase transition and behavior of the 2 3 phonon branch of Rb2SeO4 have been investigated with the use of heat capacity measurement and X-ray and neutron scattering technique. No phase transition was detected down to 2 K, both in thermal analysis and in neutron elastic scattering. However, neutron inelastic scattering showed a slight softening of the phonon excitation frequency below 100 K. Two typical trst-order-type anomalies due to the phase I - phase II transition and melting were observed at 821 K and 1233 K, respectively. The entropy change for the phase I - phase II transition was determined as 12.46 Jmol1K1.
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.
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.