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

The relative proportions of high-spin Co3+ and low-spin CoIII 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 CoIII 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 CoIII giving rise to intermediate charge-transfer states. However, ErCoO3 is quite similar to HoCoO3 with no evidence for electron transfer and both χgT and Mössbauer data show an essentially constant Co3+/CoIII ratio. Both YCoO3 and ErCoO3 show a first order localized electron-itinerant electron transition around 1200 K above which the bonding eg electrons form σ* bands.