ESR-Untersuchungen zum Jahn-Teller-Effekt des Cu2+-Ions in oxidischen Perowskiten

Abstract

Abstract The ESR-powder-spectra of the perovskite-mixed-crystals M2II (CuxZn1-xW)O6 [MII=Sr, Ba] and Sr2(CuxZn1-xTe)O6 , which have been investigated by means of conventional X-ray-techniques and ligand-field-spectroscopy 1,2, are described and the results extensively discussed. The conclusions can be summarized as follows: (a) At very low x-values isolated, dynamically Jahn-Teller-distorted CuO6-octahedra are present in the cubic matrices, which can be frozen into tetragonally elongated polyhedra at 4.2 °K; (b) At high x-values the CuO6-entities are statically JT-distorted with the long axes lined up along the c-axis of the macroscopically tetragonal phases; (c) The ESR-spectra around the cubic-tetragonal phase-transition are complex, containing signals of obviously magnetically coupled Cu2+-ions; (d) The g-values "follow" the ligand-field-parameters quantitatively. Comparative data of some other compounds are given.