Dynamic Investigations of Pressure-Induced Abnormal Phase Transitions in PbTiO3**Supported by the Fundamental Research Funds for the Central Universities under Grant No 2013RC19.

Abstract

The effects of pressure on phonon modes of ferroelectric tetragonal P4mm and paraelectric cubic Pmm PbTiO3 are systematically investigated by using first-principles simulations. The pressure-induced tetragonal-to-cubic and subsequent cubic-to-tetragonal phase transitions are the second-order transitions, which are different from the phase transitions induced by temperature [Phys. Rev. Lett. 25 (1970) 167]. As pressure increases, the lowest A1 and E modes of the tetragonal phase become softer and converge to the F1u mode of the cubic phase. As pressure further increases, the lowest F1u mode first hardens and then softens again, and finally diverges into A1 and E modes. The behaviors of optical phonon modes confirm the ferroelectric-to-paraelectric-to-ferroelectric phase transitions.