Soft mode anisotropy in negative thermal expansion material ReO${}_3$

Abstract

We use a symmetry-motivated approach to analyse neutron pair distribution function data to investigate the mechanism of negative thermal expansion (NTE) in ReO${}_3$. This analysis shows that the local structure of ReO${}_3$ is dominated by an in-phase octahedral tilting mode and that the octahedral units are far less flexible to scissoring type deformations than the octahedra in the related compound ScF${}_3$. These results support the idea that structural flexibility is an important factor in NTE materials, allowing the phonon modes that drive a volume contraction of the lattice to occupy a greater volume in reciprocal space. The lack of flexibility in ReO${}_3$ restricts the NTE-driving phonons to a smaller region of reciprocal space, limiting the magnitude and temperature range of NTE. In addition, we investigate the thermal expansion properties of the material at high temperature and do not find the reported second NTE region. Finally, we show that the local fluctuations, even at elevated temperatures, respect the symmetry and order parameter direction of the observed $P4/mbm$ high pressure phase of ReO${}_3$. The result indicates that the motions associated with rigid unit modes are highly anisotropic in these systems.

9 pages, 6 figures

References in corpus (4)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• Mantid - Data Analysis and Visualization Package for Neutron Scattering and $\mu SR$ Experiments
• Anharmonicity and scissoring modes in the negative thermal expansion materials ScF${}_3$ and CaZrF${}_6$

Cited by in corpus (3)

• Tailoring of rhenium oxidation state in ReOx thin films during reactive HiPIMS deposition process and following annealing
• Symmetry-mode analysis for local structure investigations using pair distribution function data
• The observation of bulk superconductivity in Rhombohedral ReO3 under pressure