Abstract
We explore the vibrational behavior and stability of ferroelectric under high pressure by Raman spectroscopy and second-harmonic-generation (SHG) measurements. Ab initio lattice-dynamics calculations have been employed to solve a controversy concerning the phonon-dispersion relations of and to carry out an assignment of the Raman modes. A ferroelectric to paraelectric phase transition has been observed both by Raman spectroscopy and SHG at 20.8 GPa. Contrary to , the ferroelectric soft mode of has been found to be the (2) and not the (1) mode. The calculated eigenvectors show that the (2) mode of ferroelectric is an antiphase vibration of the Ti atom against the oxygen framework, similar to the soft modes observed in ferroelectric perovskites. The SHG signal of has been found to be independent of the grain size below the phase transition, indicating that is a phase-matchable compound.
1 More- Received 15 April 2015
- Revised 1 June 2015
DOI:https://doi.org/10.1103/PhysRevB.91.214110
©2015 American Physical Society