VO2+ (3d1 ) and Cu2+ (3d9 ) are the two complementary states that usually show opposite distortions when they are doped in crystals. In this work, the optical absorption spectra (OAS), electron paramagnetic resonance (EPR) parameters, and local structure (LS) for VO2+ (and Cu2+ ) in MgNH4 PO4 ·6H2 O (MPPH) are uniformly investigated on the basis of the high-order perturbation formulas for a 3d1 (and 3d9 ) ion in tetragonally compressed (and elongated) octahedra, respectively. In the calculated formulas, the required crystal-field parameters can be obtained from the superposition model and reasonably linked with the LS distortion for VO2+ and Cu2+ centers. Based on the calculations, the tetragonal compressed [VO(H2 O)5 ]2+ cluster (and tetragonal elongated [Cu(H2 O)6 ]2+ cluster) is found to suffer tetragonal compression ratio of 1.65% and tetragonal elongation ratio of 3.8% along C4 -axis, respectively, due to the Jahn-Teller (JT) effect. The theoretical EPR parameters based on the above lattice distortions agree well with the experimental data, and the LS of the VO2+ and Cu2+ centers in MPPH is discussed.
Keywords: Cu2+; MgNH4PO4·6H2O; VO2+; electron paramagnetic resonance (EPR); optical spectra.
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