A Raman scattering study of the antiferroelectric phase transition in (Sr0.70Ca0.30)TiO3

Abstract

The Raman scattering measurements on ceramic pellets of Sr0.70Ca0.30TiO3 (SCT 30) 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.