Theory studies of the local lattice distortions and the EPR parameters for Cu2+, Mn2+ and Fe3+ centres in ZnWO4

The local lattice distortions and the electron paramagnetic resonance (EPR) parameters (g factors, hyperfine structure constants and zero-field splittings) for Cu2+, Mn2+ and Fe3+ in ZnWO4 are theoretically studied based on the perturbation calculations for rhombically elongated octahedral 3d(9) and 3d(5) complexes. The impurity centres on Zn2+ sites undergo the local elongations of 0.01, 0.002 and 0.013 angstrom along the C-2 axis and the planar bond angle variations of 8.1 degrees, 8.0 degrees and 8.6 degrees for Cu2+, Mn2+ and Fe3+, respectively, due to the Jahn-Teller effect and size and charge mismatch. In contrast to the host Zn2+ site with obvious axial elongation (similar to 0.31 angstrom) and perpendicular (angular) rhombic distortion, all the impurity centres demonstrate more regular octahedral due to the above local lattice distortions. The copper centre exhibits significant Jahn-Teller reductions for the spin-orbit coupling and orbital angular momentum interactions, characterised by the Jahn-Teller reduction factor J (approximate to 0.29 MUCH LESS-THAN 1). The calculated EPR parameters agree well with the experimental results. The local structures of the impurity centres are analysed in view of the corresponding lattice distortions.