Molecular copper centers in potassium tantalate crystals

ESR spectra with resolved hyperfine and superhyperfine structures have been recorded in the 3-cm range at 4.2–800 K for copper-doped KTaO₃ crystals. The axial centers have three orientations. The principal values have been determined for the g tensor and for the hyperfine and superhyperfine interactions tensors. The g factor is explained in a simple crystalline-field model incorporating covalency effects. An MO LCAO model is used to interpret the hyperfine structure and to determine the bond covalencies along the axis of the CuO ₄ ^2– molecular centers and also for bonds perpendicular to that axis. The numbers of lines and the magnitudes and angle dependences for the superhyperfine splittings reveal details in the molecular structure of these centers. The scope for interpreting the results in terms of Jahn-Teller centers is discussed. The measurements do not indicate features characteristic of Jahn-Teller centers, so preference is given to the molecular-center model.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 562–568, September–October, 1988.