Spin state equilibria and localized versus collective d-electron behaviour in neodymium and gadolinium trioxocobaltate(III)

Abstract

Magnetic susceptibility measurements and mossbauer spectra show that NdCoO₃ and GdCoO₃ contain predominantly low-spin Co^III ions at low temperatures which transform partially to high-spin Co³⁺ until a certain temperature. Beyond this temperature, there is a transfer of e_g electrons from Co³⁺ to Co^III giving rise to di- and tetra-valent Co species followed by short-range ordering. Co³⁺ ions completely disappear at about 1000 K where there is a gradual transition from localized electron behaviour to collective behaviour. The cobaltates are semi-metals beyond this transition. The spin state equilibria and the electronic transition described here find support from electron transport properties, mossbauer parameters as well as differential thermal analysis and x-ray data.