Studies of the Local Distortions for Cu 2+ in Ba 2 Zn(HCOO) 6 ·4H 2 O Single Crystal

Abstract

The high-order perturbation formulas of the electron paramagnetic resonance (EPR) parameters for an orthorhombically elongated octahedral 3d9 cluster are adopted to analyze the local distortions of divalent copper in Ba2Zn(HCOO)6·4H2O (BZFA). The doped Cu2+ may substitute the host Zn2+ in the lattice, with different local environments from the original Zn2+, which can strongly affect its EPR parameters. In the calculations, the admixture of d-orbitals in the ground state for the impurity Cu2+ ion under orthorhombic symmetry is considered, and the required molecular orbital coefficients are determined from the cluster approach. The orthorhombic field parameters are correlated with the local lattice distortion (characterized by the axial elongation δz and the relative perpendicular bond length variation δr) and can be calculated from the superposition model. The theoretical EPR parameters based on the above local structure are in good agreement with the observed values, and the results are discussed.