Theoretical studies of the spin Hamiltonian parameters and the local structure for the orthorhombic V4+ in CaYAlO4

The spin Hamiltonian parameters (g-factors and the hyperfine structure constants) and the local structure tor the orthorhombic V4+ in CaYAlO4 are theoretically studied from the perturbation formulas of these parameters for a 3d(1) ion in ortho-rhombically distorted octahedra. Based on the present studies, this center is explicitly assigned to V4+ occupying the Al3+ site, associated with one next-nearest-neighbor Mg2+ replacing the host Al3+ (i.e. Mg-Al) in the ab-plane due to the charge compensation. Since the effective charge of the compensator is negative ( e), the ligand O2- intervening in the impurity V4+ and the Mg-Al would undergo a small displacement (approximate to 0.08 angstrom) towards the central ion because of the electrostatic repulsion. The local structure of this center can be described as elongation of the oxygen octahedron along the c-axis and the slight orthorhombic distortion in the perpendicular direction. The theoretical spin Hamiltonian parameters and the optical transitious based on the above local structure show reasonable agreement with the experimental data.