The various phases of the system Sr1-xCaxTiO3—A Raman scattering study

This paper deals with the structural Raman-active and the disorder-induced TO and LO Raman modes in Sr1-xCaxTiO3 (SCT) ceramics. Spectra were recorded at ambient pressure in a wide range of temperatures from 8 K up to 500 K. The chemical composition (x) was chosen so as to investigate the phase boundaries which have been previously determined in the x-T phase diagram. An eigenvector analysis is given for all the known phases. The Raman data confirm the occurrence of a double-tilt system of Imma space group lying between the tetragonal I4/mcm and the orthorhombic Pbnm structures for x >= 0.06. Higher-order transformation of the anti ferroelectric phase (0.20 <= x <= 0.40) at low temperature is also suggested. The main interesting disorder-induced effects originate from the temperature behaviour of the hard polar modes TO2 and TO4, which appear in the Raman spectra of the paraelectric domain. This behaviour allows one to discuss the precursor range of ferroelectricity in the SCT system in terms of ferroelectric- or antiferroelectric-type dipolar interactions. Copyright (c) 2005 John Wiley & Sons, Ltd.