Valence-state and spin-state transition of Co in LaC o0.5 R h0.5 O3

We have observed that the Rh substitution for Co in LaCo0.5Rh0.5O3 leads to the spectral feature at the Co-L2,3 absorption edge taken at 300 K similar to that in LaCoO3 taken at 650 K, in which the spin state of magnetic Co3+ ions has been controversially discussed in the past decades and can be easily clarified by studying LaCo0.5Rh0.5O3 without worrying about oxygen loss induced at high temperature. Our combined experimental and theoretical x-ray absorption spectroscopy (XAS) at the Co-L2,3 and the experimental Rh-L2,3 edges indicated a nearly 1:1 mixture of high-spin (HS) and low-spin (LS) Co3+(3d6) and a LS Rh3+(4d6) in contrast to the Co2+/Rh4+ state found in Ca3CoRhO6 at room temperature. Upon cooling only a small portion of the HS Co3+ ions was converted to a LS state until 10 K in LaCo0.5Rh0.5O3. The Co-Kβ x-ray emission spectra revealed a gradual spin-state transition from a mixed LS/HS at ambient pressure to a complete LS state of Co3+ ions up to 14 GPa. The theoretical and experimental intensity ratio I(L3)/I(L2) on the Co-L2,3 edges and a comparison between the difference spectrum of Kβ x-ray emission of LaCo0.5Rh0.5O3 taken at ambient pressure (AP) and 14 GPa and that of Sr2CoRuO6 taken at AP and 39.6 GPa exclude the intermediate spin state of Co3+ in LaCo0.5Rh0.5O3.