Department of Earth and Space Science,Graduate School of science, Osaka University^* Department of Earth and Space Science, Graduate School of science, Osaka University, Japan^** Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Japan^***
○Hiroaki Sugita^* Hiroaki Sugita^** Hiroshi Matsumura^* takamitsu Yamanaka^*** Yuki Nakamoto^***

BaTiO₃ and PbTiO₃ perovskite are known as ferroelectrics at ambient conditions, and are used as electronic materials in various fields. Both have phase transitions by applying pressure, from tetragonal structure (P4mm Z=1) to cubic structure (Pm3m Z=1). The former is a ferroelectric phase, and the latter a paraelectric phase.
In order to understand a change of a dipole moment, dielectric efficiency and dielectric capability under high-pressure or low-temperature conditions, we carried out electron density analysis by single crystal diffraction experiment using synchrotron radiation and diamond-anvil cell (DAC).
BaTiO₃ and PbTiO₃ single crystals are synthesized by a flux method. We used a modified Merrill and Bassett type DAC for generating pressure. We conducted single-crystal X-ray diffraction experiment at ambient temperature under pressure from 0.0001GPa to 5GPa in BaTiO₃, from 0.0001GPa to 9.3GPa in PbTiO3. Moreover in BaTiO₃, we executed an experiment at low temperatures (20℃~-170℃) and ambient pressure, and further at various low temperature under compression.
We determined a dipole moment by electron density and radius distribution between atoms at each pressure. This study revealed a pressure dependence of anisotropy of a dipole moment of BaTiO₃ accompanied by successive phase transitions; cubic to tetragonal to orthorhombic to rhombohedral at low temperatures.