Effect of the rare earth ion on the spin state equilibria in perovskite rare earth metal cobaltates. Yttrium trioxocobaltate(III) and erbium trioxocobaltate(III)

Abstract

The relative proportions of high-spin Co³⁺ and low-spin Co^III in HoCoO₃ are about 1:1 at temperatures above 300 K, while in the lighter rare earth metal cobaltates, there is evidence for appreciable charge-transfer from Co³⁺ to Co^III producing intermediate states. We have investigated the effect of the size of the rare earth metal ion on the electronic and magnetic properties of cobaltates by examining YCoO₃ and ErCoO₃ in some detail. Mössbauer studies show that the properties of YCoO₃ are similar to those of the lighter rare earth metal cobaltates in that there is considerable electron transfer from Co³⁺ to Co^III giving rise to intermediate charge-transfer states. However, ErCoO₃ is quite similar to HoCoO₃ with no evidence for electron transfer and both χ_gT and Mössbauer data show an essentially constant Co³⁺/Co^III ratio. Both YCoO₃ and ErCoO₃ show a first order localized electron-itinerant electron transition around 1200 K above which the bonding e_g electrons form σ* bands.