Theory studies of the local lattice distortions and the EPR parameters for Cu , Mn and Fe centres in ZnWO 4.

The local lattice distortions and the electron paramagnetic resonance (EPR) parameters (gfactors, hyperfine structure constants and zero-field splittings) for Cu2+, Mn2+and Fe3+in ZnWO4are theoretically studied based on the perturbation calculations for rhombically elongated octahedral 3d9and 3d5complexes. The impurity centres on Zn2+sites undergo the local elongations of 0.01, 0.002 and 0.013 Å along the C2axis and the planar bond angle variations of 8.1°, 8.0° and 8.6° 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 (∼0.31 Å) 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 factorJ(≈0.29 ≪ 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. [ABSTRACT FROM AUTHOR]