Electron spin resonance evidence for the role of copper ions in interlayer coupling in layered copper oxycarbonates

Article abstract of DOI:10.1016/0921-4534(93)90702-R

Electron spin resonance (ESR) studies have been carried out on the layered copper oxycarbonates (alternating layers of CuO₂ and CO₃^2-) with the nominal composition Ba₃SrCu₂O₆.2CO₂ and their reaction products with ammonium slats. The ESR signals typical of copper ions in square-planar geometry with a slight orthorhombic distortion presumably arise from the copper ions being incorporated in the carbonate layer. A simple grinding procedure at room temperature using (NH₄⁺)_nX^n- (X=F^-, (NO₃)^-, (VO₃)^-, (HPO₄)^2-) incorporates X^n- anions in the structure with the liberation of ammonia. The environment of the copper ion in the carbonate layer is thus changed without altering the structure. The g₃ values are most affected by this reaction showing that the filled e_g orbitals are oriented in the plane of the carbonate layer. The half-filled e_g orbitals (transforming as d_x(2)-y(2) orbitals) are oriented out of the plane. This suggests that the copper ions in the carbonate layers are probably involved in introducing magnetic coupling between the CuO₂ layers.