Bond valence calculation for several perovskites and the evidences for a valence charge transfer process in these compounds

Abstract

This paper presents the bond valence calculation for several perovskite systems and describes the evidences for a valence charge transfer process in these compounds. The reviewing of the crystal structures of La1-xPbxMnO3 (x=0.1-0.5), La0.6Sr0.4-xTixMnO3 (x=0.0-0.25) and La1-xSrxCoO3 (x=0.1-0.5) is also presented. On the basis of testing samples, the distribution of valence charge has been evaluated which showed the failure of elastic bonding mechanism on all studied systems and revealed the general deficit of valence charge in the unit cell. This deficit was not equally localized on all coordination spheres but proved asymmetrically distributed between the spheres. As the content of substitution increased, the charge deficit declined systematically from balanced level, signifying the continuous transfer of valence charge from the B-O6 to A-O12 spheres. The transfered charge varied from system to system, depending on the valence deviation of spheres and was not small. The total valence deviation reached near 2electron/unit cell in the studied systems. The local deviation may be more larger than this average value. The possible impact of the limitted accuracy of the available structural data on the bond valence results has been considered.