Pressure-induced structure transition and the pressure dependence of electron density distribution in BaTiO3 and PbTiO3 perovskite ferroelectrics

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.