Theoretical prediction of negative thermal expansion in cubic VF3

Abstract

Designing and discovering negative thermal expansion (NTE) materials is important in precisely controlled thermal expansion devices. In this work, the NTE of a cubic metal fluoride, ReO₃-type VF₃, was predicted by density functional theory within the quasi-harmonic approximation. These results reveal that cubic VF₃ displays a negative thermal expansion behavior below 200 K, and the predicted minimum negative thermal expansion coefficient is approximately −6.4 × 10⁻⁶ K⁻¹ at 80 K. The negative thermal expansion was mainly dominated by the prominently negative Grüneisen parameter situated at M(0.5,0.5,0) and R(0.5,0.5,0.5). The underlying mechanism was attributed to the anisotropic F atom vibration, where the amplitude of transverse vibration perpendicular to the V–F–V connection was much larger than that of the vibration along the parallel V–F–V direction. This research provides a good understanding of the relationship between NTE and crystal structure.