Structural anomalies, spin transitions and charge disproportionation in LnCoO3

TL;DR

This paper presents a new model for understanding the spin state transitions and charge behavior in LnCoO3 perovskites, emphasizing a LS-HS-IS scenario that explains their magnetic and electronic phase changes.

Contribution

It introduces a novel LS-HS-IS two-level excitation model for LnCoO3, differing from previous models by explicitly incorporating interatomic electron transfer and spin state stabilization.

Findings

Quantified model parameters for La, Pr, Nd samples using neutron diffraction.

Interpreted magnetic susceptibility data for LaCoO3 and YCoO3.

Reinterpreted insulator-metal and magnetic transitions 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 LS-HS-IS (low-high-intermediate spin) 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.