Spin state of Co$^{3+}$ in LaCo$_{1-x}$Rh$_{x}$O$_{3}$ investigated by structural phenomena

TL;DR

This study investigates the spin state of Co$^{3+}$ in LaCo$_{1-x}$Rh$_{x}$O$_{3}$ using neutron and x-ray diffraction, revealing a mixed high-spin and low-spin state influenced by temperature and Rh substitution.

Contribution

It provides new insights into the spin state behavior of Co$^{3+}$ ions in Rh-doped LaCoO$_{3}$ through detailed structural analysis.

Findings

Co(Rh)-O bond lengths are nearly identical at 10 K.

Lattice volume decreases with temperature and stabilizes around 70 K.

High-spin Co$^{3+}$ ions are thermally excited and influenced by Rh substitution.

Abstract

Neutron diffraction for a polycrystalline sample of LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$ and synchrotron x-ray diffraction for polycrystalline samples of LaCo$_{0.9}$Rh$_{0.1}$O$_{3}$ and LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$ have been carried out in order to investigate the structural properties related with the spin state of Co$^{3+}$ ions. We have found that the values of the Co(Rh)-O bond lengths in the Co(Rh)O$_{6}$ octahedron of LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$ are nearly identical at 10 K. The lattice volume for the Rh$^{3+}$ substituted samples decreases with the thermal expansion coefficient similar to that of LaCoO$_{3}$ from room temperature, and ceases to decrease around 70 K. These experimental results favor a mixed state consisting of the high-spin-state and low-spin-state Co$^{3+}$ ions, and suggest that the high-spin-state Co$^{3+}$ ions are thermally excited in addition to those pinned by the substituted Rh$^{3+}$ ions.