Investigation of the local geometry and EPR parameters of V3+ and Cr4+ centers in Al2O3 crystals

Abstract

The EPR parameters (zero-field splitting D and g factors g∥, g⊥) of 3d2 V3+ and Cr4+ centers in Al 2O3 crystals are calculated by using the diagonalization of the complete energy matrix for 3d2 ions in trigonal symmetry. The crystal-field parameters are estimated for the superposition model related to the local geometry (or structure) of the impurity centers. From the calculations, the EPR parameters for both impurity centers are explained and the local structures (characterized by the impurity displacement Δz along the C3 axis and the displacement Δx of O2- ions in the oxygen triangle between the impurity and the vacant oxygen octahedron along the x-axis, resulting from the electrostatic repulsive force and the electronic cloud overlap) of these impurity centers are estimated. The results are discussed. © 2006 Verlag der Zeitschrift für Naturforschung,.