A Raman scattering study of the antiferroelectric phase transition in (Sr_0.70Ca_0.30)TiO3₃

Abstract

The Raman scattering measurements on ceramic pellets of Sr_0.70Ca_0.30TiO₃ (SCT30) have been carried out as a function of temperature from 290 K to 8 K. It is shown that below (236 ± 5 K) , two additional lines appear around 79 and 128 cm⁻¹ . Further, there is enhancement in the intensity of the modes near 170 and 541 cm⁻¹ below (236 ± 5 K) . The temperature at which these changes occur in the Raman spectra of SCT 30 correlates very well with the temperature at which the antiferroelectric superlattice reflections appear in the x-ray diffraction patterns. We propose that the additional modes are due to q ≠ 0 phonons that have become Raman active due to the folding of the corresponding special points into the zone center below the cell-doubling antiferroelectric phase-transition temperature.