Phase transition of SrTiO₃ under high pressure

Abstract

The Raman spectrum of SrTiO₃ as a function of hydrostatic pressure up to 15 GPa was studied at room temperature. The structural phase transition of cubic to tetragonal phase occurred at p_c = 6.4 GPa. In the high pressure phase four first-order Raman active modes, i.e. two soft A_lg and E_g modes and two high frequency E_g and B_lg modes were observed. The second-order Raman modes decreased in intensity with increase of pressure and disappeared at 13 GPa. The high frequency E_g and B_lg modes increased in intensity with pressure. The soft A_lg and E_g mode frequencies were analysed with the expression ω² = ω₀ ²(p/p_c - 1) with ω₀ = 82.4 cm⁻¹ for A_lg and 33.4 cm⁻¹ for E_g . The result was discussed on the basis of the phenomenological theory.

Key Words:

• high pressure Raman scattering
• structural phase transition
• soft mode
• SrTiO₃