Soft-mode study of the stress-induced phase transitions near T₀ in SrTiO₃

We have studied the stress-induced phase transitions of SrTiO₃ in the vicinity of T₀, by means of softmode Raman scattering. Theoretical expressions for the soft-mode frequencies, critical stresses, and linear displacements of the vibrating atoms are described in terms of the phenomenological theory. Experimental results of soft-mode frequencies versus stress in the [111] direction, for temperatures both below and above T ₀ are given. The temperature dependence of the coefficient of the harmonic force, in the vicinity of T₀ is shown and discussed. Critical stresses for temperatures T>T₀ are measured, and the equilibrium values of the linear displacements of the vibrating atoms are derived from the experimental results.