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Synthesis and electrical conductivity of bulk tetra-valent cerium pyrophosphate
Hiroaki Onoda,Yousuke Inagaki,Akihide Kuwabara,Naoto Kitamura,Koji Amezawa,Atsushi Nakahira,Isao Tanaka 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.3
Tetra-valent cerium pyrophosphate was synthesized from cerium oxide and phosphoric acid by heating. The sintering processes, pressure-less sintering (PLS), spark plasma sintering (SPS), and hydrothermal hot pressing (HHP), were attempted to form bulk pyrophosphate. Furthermore, the electrical conductivity of bulk cerium pyrophosphate was investigated. Tetravalent cerium pyrophosphate was synthesized by heating at 700 oC for 20 hours. The hydrothermal hot pressing process was a suitable method to synthesize bulk tetra-valent cerium phosphate.
First-Principles Calculations of Phase Transition in CaTiO_3 under Negative Static Pressure
Hiroki Moriwake,Craig A. J. Fisher,Akihide Kuwabara,Tetsuya Tohei,Isao Tanaka 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
The relative enthalpy among different structure of CaTiO_3 under negative static pressure is studied by means of first-principles calculations. At zero pressure, the lowest energy structure calculated for CaTiO_3 was the same as that found experimentally at low temperatures, namely the Pnma orthorhombic phase. However, below -8.5 GPa, the symmetry of the lowest energy structure changes from non-ferrroelectric Pnma to ferroelectric P4mm, corresponding to a ferroelectric phase transition under negative static pressure. The P4mm structure was, however, found to be dynamically unstable by lattice dynamics calculation. This implies formation of lower symmetry structure under negative hydrostatic pressure.