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Abstract:
We explore the vibrational behavior and stability of ferroelectric ZnTiO3 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 ZnTiO3 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 LiNbO3, the ferroelectric soft mode of ZnTiO3 has been found to be the A1(2) and not the A1(1) mode. The calculated eigenvectors show that the A1(2) mode of ferroelectric ZnTiO3 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 ZnTiO3 has been found to be independent of the grain size below the phase transition, indicating that ZnTiO3 is a phase-matchable compound.
