Lattice dynamics of perovskite PbxCa1-xTiO3

Abstract

Investigation of the structural and vibrational properties of the PbxCa1-xTiO3 (PCT) system exhibits two phase transitions in the range of x=0-1 by using x-ray powder diffraction and Raman spectroscopy. The first transition occurring at xsimilar to0.65 corresponds to the tetragonal-to-cubic phase and the second one occurs near x=0.35 is attributed to the orthorhombic-to-cubic phase. The absence of the intermediate tetragonal phase between orthorhombic and cubic phases (0<x<0.35) may be mostly attributed to the very restricted region in the PCT system. In addition, a decreasing giant LO-TO splitting behavior similar to that exhibited in PbxSr1-xTiO3 system for lower Pb concentration was also observed, which has been attributed to the highly Pb-O covalent bonding to reduce the long-range Coulomb interaction. Comparison of the change of line shapes of A(1)(1TO) mode among three PbTiO3-based perovskites indicates that the anharmonicity will become more conspicuous due to the larger high-order potential terms of Ba2+ and Ca2+ substitution than Sr2+ substitution for Pb2+.