The role of static disorder in negative thermal expansion in ReO3

TL;DR

This study investigates how static disorder influences negative thermal expansion in ReO3, revealing that static disorder correlates with reduced NTE and that ReO3 lacks low-energy modes typical of other NTE oxides.

Contribution

It demonstrates the impact of static disorder on NTE in ReO3 and shows how sample preparation affects thermal expansion behavior.

Findings

ReO3 exhibits negative thermal expansion at low temperatures.

Static disorder in oxygen atoms correlates with diminished NTE.

ReO3 does not have low-energy Einstein modes like other NTE oxides.

Abstract

Time-of-flight neutron powder diffraction and specific heat measurements were used to study the nature of thermal expansion in rhenium trioxide, an electrically conducting oxide with cubic symmetry. The temperature evolution of the lattice parameters show that ReO3 can exhibit negative thermal expansion at low temperatures and that the transition from negative to positive thermal expansion depends on sample preparation; the single crystal sample demonstrated the highest transition temperature, 300 K, and largest negative value for the coefficient of thermal expansion, alpha = -1.1(1)x 10^-6 K^-1. For the oxygen atoms, the atomic displacement parameters are strongly anisotropic even at 15 K, indicative of a large contribution of static disorder to the displacement parameters. Further inspection of the temperature evolution of the oxygen displacement parameters for different samples reveals that the static disorder contribution is greater for the samples with diminished NTE behavior. In addition, specific heat measurements show that ReO3 lacks the low energy Einstein-type modes seen in other negative thermal expansion oxides such as ZrW2O8.