Anomalous expansion and phonon damping due to the Co spin-state transition in RCoO_3 with R = La, Pr, Nd and Eu

TL;DR

This study investigates how spin-state transitions in RCoO_3 perovskites influence thermal expansion and phonon damping, revealing the role of different R ions and crystal field effects on heat transport.

Contribution

It provides a detailed analysis of the impact of spin-state transitions and crystal field splitting on thermal properties across the RCoO_3 series, with a quantitative model for thermal conductivity.

Findings

Spin-state transition affects thermal expansion and phonon scattering.

Higher spin states suppress phonon thermal conductivity.

Resonant phonon scattering occurs due to 4f level splitting in PrCoO_3.

Abstract

We present a combined study of the thermal expansion and the thermal conductivity of the perovskite series RCoO_3 with R = La, Nd, Pr and Eu. The well-known spin-state transition in LaCoO_3 is strongly affected by the exchange of the R ions due to their different ionic radii, i.e. chemical pressure. This can be monitored in detail by measurements of the thermal expansion, which is a highly sensitive probe for detecting spin-state transitions. The Co ions in the higher spin state act as additional scattering centers for phonons, therefore suppressing the phonon thermal conductivity. Based on the analysis of the interplay between spin-state transition and heat transport, we present a quantitative model of the thermal conductivity for the entire series. In PrCoO_3, an additional scattering effect is active at low temperatures. This effect arises from the crystal field splitting of the 4f multiplet, which allows for resonant scattering of phonons between the various 4f levels.