Phase Stability of Multiferroic GaFeO3 up to 1368 K from In situ Neutron Diffraction

TL;DR

This study uses in situ neutron diffraction to show that GaFeO3 remains structurally stable up to 1368 K, with no phase transition, and provides insights into how temperature affects its multiferroic properties.

Contribution

It provides the first detailed high-temperature structural analysis of GaFeO3, revealing stability and site disorder behavior up to 1368 K, and links structural features to polarization changes.

Findings

No structural transition observed up to 1368 K

Site disorder remains nearly unchanged with temperature

Electric polarization decreases as temperature increases

Abstract

We report a detailed high-temperature powder neutron diffraction investigation of the structural behavior of the multiferroic GaFeO3 between 296 and 1368 K. Temperature dependent neutron diffraction patterns do not show any appreciable change either in intensity or appearance/disappearance of the observed peaks upto 1368 K, ruling out any structural transition in the entire temperature range. The lattice parameters and volume exhibit normal thermal expansion behaviour, indicating the absence of any structural changes with increasing temperature. The origin of the magnetoelectric couplings and multiferroicity in GaFeO3 is known to be influenced by the site disorder from Ga/Fe atoms. Our analysis shows that this disorder remains nearly the same upon increase of temperature from 296 to 1368 K. The structural parameters as obtained from Rietveld refinement of neutron diffraction data are used to calculate the interatomic distances and distortions of the oxygen polyhedra around the Ga1, Ga2, Fe1 and Fe2 cations. Evolution of the distortion of the oxygen polyhedra around these sites suggests that the Ga1-O tetrahedron is least distorted and Fe1-O is most distorted. Structural features regarding the distortion of polyhedral units would be crucial to understand the temperature dependence of the microscopic origin of polarizations. The electric polarization has been estimated using a simple ionic model and its value is found to decrease with increasing temperature.