Studies of the Local Distortions for Cu2+ in Ba2Zn(HCOO)6·4H2O 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.