Investigations on the Spin-Hamiltonian Parameters and Local Structure of the Orthorhombic Cu2+ Center in PbTiO3 Crystal.

The spin-Hamiltonian parameters (the g factors g_i and the hyperfine structure constants A_i, i = x, y, z) and local structure of the Cu²⁺ center in PbTiO₃ are theoretically studied by using the perturbation formulae of these parameters for a 3d⁹ ion in an orthorhombically elongated octahedra. The orthorhombic center is attributed to Cu²⁺ occupying the host Ti⁴⁺ site associated with a nearest-neighbouring oxygen vacancy V_O along the c-axis, and the impurity Cu²⁺ off-center displacement ΔZ_L (≈0.18 Å) is smaller than that of the host Ti⁴⁺ site (ΔZ_H ≈ 0.3 Å). Meanwhile, the planar Cu²⁺-O^2- bonds are found to experience the relative variation ΔR (≈ 0.098 Å) along the a- and b-axes, respectively, due to the Jahn-Teller effect and the size mismatching substitution of Ti⁴⁺ by Cu²⁺. The theoretical spin-Hamiltonian parameters based on the above defect structure agree well with the observed values. [ABSTRACT FROM AUTHOR]