Decreasing giant splitting of longitudinal and transverse optical phonons in PbxSr1-xTiO3 due to Pb covalency

Abstract

In contrast to the increase of giant splitting of longitudinal optical (LO) and transverse optical (TO) phonons in polycrystalline BaxSr1-xTiO3 [Phys. Rev. B. 64, 224103-1 (2001)], a decreasing splitting of the softest A(1)(1TO) and the hardest A(1)(3LO) was observed in PbxSr1-xTiO3. A similar structure but anomalous discrepancies in lattice dynamics of ABO(3) perovskite are related to the diverse electronic states of Pb2+ and Ba2+ ions. In this article, Pb-O interaction is proposed to be more hybridized than Ba-O, and thus the change of effective charge to the LO-TO splitting may be the dominant mechanism in PbxSr1-xTiO3, while unit-cell volume change is in the BaxSr1-xTiO3 systems. (C) 2002 American Institute of Physics.