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

Abstract

Abstract The ESR-powder-spectra of the perovskite-mixed-crystals M 2 II (CuxZn 1 -x W)O 6 [M II =Sr, Ba] and Sr 2 (Cu x Zn 1 -x Te)O 6 , 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 CuO 6 -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 CuO 6 -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 Cu 2+ -ions; (d) The g-values "follow" the ligand-field-parameters quantitatively. Comparative data of some other compounds are given.