Structural anomalies, spin transitions, and charge disproportionation in LnCoO3

Abstract

The diamagnetic-paramagnetic and insulator-metal transitions in LnCoO3 perovskites (Ln=La,Y, rare earths) are reinterpreted and modeled as a two-level excitation process. In distinction to previous models, the present approach can be characterized as a low-high-intermediate spin LS-HS-IS scenario. The first level is the local excitation of HS Co3+ species in the LS ground state. The second excitation is based on the interatomic electron transfer between the LS/HS pairs, leading finally to a stabilization of the metallic phase based on IS Co3+. The model parameters have been quantified for Ln=La, Pr, and Nd samples using the powder neutron diffraction on the thermal expansion of Co–O bonds that is associated with the two successive spin transitions. The same model is applied to interpret the magnetic susceptibility of LaCoO3 and YCoO3.