Structural phenomena associated with the spin-state transition in LaCoO3

TL;DR

This study investigates how spin-state transitions in LaCoO3 influence its structural properties across a wide temperature range, revealing effects on lattice parameters, bond lengths, and oxygen vacancy formation.

Contribution

It provides detailed neutron diffraction data and a quantitative model of spin-state effects, including the identification of a third lattice anomaly linked to oxygen vacancies.

Findings

Spin-state transitions affect unit cell volume and bond lengths.

Intermediate-spin state has a smaller ionic radius (~0.56 Å) than low/high-spin states (~0.58 Å).

A lattice anomaly around 800 K suggests oxygen vacancy formation.

Abstract

The structural properties of LaCoO3 were studied by means of high-resolution neutron powder diffraction in the temperature range 5<T<1000 K. Changes of the Co+3 spin states in this temperature interval are shown to affect not only the unit cell volume, as previously known, but also internal parameters such as the metal-oxygen bond lengths. These data, as well as the temperature-dependent magnetic susceptibility, can be qualitatively modeled based on a 3-state (low-spin, intermediate-spin and high-spin) activated behavior, but correction terms are required for quantitative agreement. Our fits consistently indicate that the ionic radius of the intermediate-spin state (~0.56 Angstroms) is smaller than the low-spin/high-spin average (~0.58 Angstroms). We also present evidence of a third lattice, anomaly, occurring around 800 K, which we attribute to the formation of oxygen vacancies.