Structural and electronic properties of PbZr_xTi_1-xO₃ (x = 0.5, 0.375): A quantum chemical study

The structural and electronic properties of the PZT materials PbZr_0.5Ti_0.5O₃ and PbZr_0.375Ti_0.625O₃ were studied by means of a Hartree-Fock quantum chemical semiempirical method that employs a periodic large unit cell (LUC) model. The atomic relaxation observed upon introduction of the Zr impurities resulted in outward oxygen atom displacements along the <100> direction for the cubic phases and varied oxygen and lead atom movements for the tetragonal structures. For these materials, the conduction bands (CB) were composed mainly of Pb 6p atomic orbitals with less important contributions of Zr 4d and Ti 3d states. The upper valence band (UVB) for the cubic phases was mostly Pb 6s in nature, with minor contribution of O 2p atomic orbitals. The tetragonal phase on the other hand was formed by Pb 6s with some contribution of admixed O 2p with Zr s atomic orbitals. The optical band gap (ΔSCF method) was found to decrease going from the cubic to the tetragonal phase in both titanates.