Theoretical Investigations on the Anomaly of the g Factors and Local Structure for LaCuO3−δ

The anomaly of the g factors and local structure for LaCuO 3− δ are theoretically investigated from the perturbation formulas of the g factors for a 3 d 9 ion in tetragonally distorted tetrahedra based on the cluster approach including the ligand contributions. The anomaly ( g ∥ >2> g ⊥ ) of the g factors is ascribed to the paramagnetic Cu 2+ (originating from the host diamagnetic Cu 3+ capturing one electron under oxygen deficiency) in a tetragonally elongated tetrahedron. The tetragonal distortion angle is found to be about 3.56° (i.e., the Cu 2+ –O 2− bond angle related to the C 4 axis is 3.56° smaller than that (≈54.74°) of a regular tetrahedron) due to the Jahn–Teller effect. The coordination number decreases from the original six for the host octahedral Cu 3+ in LaCuO 3− δ to four for the tetrahedral impurity Cu 2+ in LaCuO 3− δ arising from incomplete Cu 2+ –O 2− bonding due to oxygen deficiency and some Cu 2+ locating in the surface of the sample.