G. Rama Rao

Rare earth cobaltite catalysts: Relation of activity to spin and valence states of cobalt

Catalytic activities of rare earth cobaltites and related compounds are shown to be related to the spin and valence states of cobalt.

Semiconductor-metal transitions in NbO2 and Nb1−xVxO2

Abstract NbO2, Nb0.98V0.02O2, and Nb0.95V0.05O2 transform from semiconducting to metallic state at temperatures higher than the DTA phase-transition temperatures. Vibrational mode softening and c-axis NbNb pairing appear to be important factors in the mechanism of these transitions. In the solid solutions, c a ratio is maximum at x = 0.5 since the metal-metal interaction along the c axis becomes minimum; conductivity is minimum at this composition since there are no mobile electrons.

Semiconductor-metal transition in v-doped Ti3O5

Abstract The semiconductor-metal transition in Ti3O5 is significantly affected by vanadium doping. The unit cell volume, ΔH, Δϱ as well as ΔχM decrease markedly up to 0.1% V3O5 and gradually thereafter until at ∼ 10% V3O5, the transition disappears.

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. Mossbauer 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 Mossbauer 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.