Abstract
ABSTRACT The electron paramagnetic resonance (EPR) parameters of the impurity Ni3+ (and Cu2+) in MgNH4PO4·6H2O (MAPH) are theoretically studied from the perturbation formulas for 3d7 (and 3d9) ions under orthorhombically compressed (and elongated) octahedra, respectively. In the above formulas, the related molecular orbital coefficients are quantitatively determined from the cluster approach in a uniform way. In the calculation model, the impurity Ni3+ and Cu2+ ions were ascribed to occupy the host octahedral Zn2+ site, the required crystal-field parameters are correlated with the local structures of the impurity Ni3+ and Cu2+ in MAPH. Based on calculation, the compressed [NiO6]9- cluster (and elongated [CuO6]10- cluster) are found to suffering the axial compression of 0.051 Å (and elongation of 0.125 Å) along z-axis, meanwhile, the planar bonds are found to experience the relative variations of 0.028 Å (and 0.05 Å), respectively, due to the Jahn–Teller effect. The theoretical EPR parameters based on the above lattice distortions agree well with the experimental data, and the local structures of the Ni3+ and Cu2+ in MAPH are discussed.
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