Investigations on the defect structures and the g factors for the two orthorhombic Ti3+ centers in CaYAlO4

The defect structures and the g factors for the two orthorhombic Ti3+ centers (A and B) in CaYAlO4 are theoretically investigated from the perturbation formulas of the g factors gξ, gη and gξ for a 3d1 ion in orthorhombically distorted octahedra. The centers may be attributed to Ti3+ locating on the Al3+ site associated with one nearest-neighbouring oxygen vacancy (VO) along the z (or c) axis and additional next-nearest-neighbouring Ti4+ replacing the host Al3+ (TiAl, i.e., center A) or Al3+ vacancy (VAl, i.e., center B) perpendicular to the c axis, respectively. Due to the electrostatic interactions arising from the local charge mismatch, the central Ti3+ undergoes a large displacement ΔZ away from the VO in the c axis, while the ligand O2− intervening in the Ti3+ and TiAl (or VAl) suffers a small outward (or inward) shift ΔX in the corresponding c plane related to the center of oxygen octahedron. The theoretical g factors for both centers based on the above displacements are in reasonable agreement with the observed values.