Investigation of the Spin Hamiltonian Parameters and the Local Structure of Two Ni3+ Centers in KTaO3

The spin Hamiltonian anisotropic g factors g∥ and g⊥ and the local structures of the Ni3+ centers I and II in KTaO3 are theoretically investigated by using the perturbation formulas of the spin Hamiltonian parameters for 3d7 ions in tetragonally distorted octahedrons and dodecahedrons. By analyzing the electron paramagnetic resonance data of the studied systems, the centers I and II can be attributed to Ni3+ ions occupying octahedral Ta5+ (associated with a nearest-neighbour oxygen vacancy VO along the C4 axis) and the dodecahedral K+ (associated with a nearest-neighbour interstitial oxygen OI along the C4 axis) sites, respectively. Based on these studies, it is found that at the center I the impurity Ni3+ is displaced away from VO by ΔZI ≈ −0.31(2) Å along the C4 axis. At the center II a large off-center displacement, ΔZII ≈ 1.12(2) Å , towards the OI along the C4 axis is obtained, due to Ni3+-OI covalent bonding.