Evolution of electronic states in RCoO₃ (R=rare earth): Heat capacity measurements

The electronic phase diagram of RCoO₃ (R=rare-earth) perovskites has been mapped out through high-pressure synthesis and heat capacity (C_p) measurements. In contrast to R=La where the spin-state transition and insulator-metal transition each shows a broad C_p anomaly, these anomalies merge into a large C_p peak for smaller R. A detailed structural study employing synchrotron x-ray powder diffraction shows that the onset temperature for the spin-state transition is correlated with the σ^*-bonding e_g bandwidth. A possible scenario on the spin state is provided to explain the C_p anomaly and phase diagram.