First-principles investigation of elastic anomalies in niobium at high pressure and temperature

TL;DR

This study uses first-principles calculations to reveal elastic anomalies and softening in niobium under high pressure and temperature, linked to electronic structure changes, with implications for its elastic properties.

Contribution

It uncovers two distinct elastic anomalies in niobium at high pressures and explains their electronic origins, including the role of thermo-electrons, which was previously unrecognized.

Findings

Elastic softening in C44 and C' at 20-150 GPa

Novel softening in C44 from 275-400 GPa

Temperature reduces elastic anomalies and induces hardening

Abstract

Niobium does not show any structure transition up to very high pressures. Nonetheless, by using density functional theory, we demonstrate in this work that it exhibits striking softening in elastic moduli C44 and C' at a pressure from 20 to 150 GPa. A novel anomaly softening in C44 from 275 to 400 GPa is also predicted. The physics behind these two anomalies is elaborated by electronic structure calculations, which revealed that they are actually different, with the first one directly relates to an underlying rhombohedral distortion whereas the latter originates in an electronic topological transition. The large magnitude of the softening leads to a remarkable elastic anisotropy in both the shear and the Young's moduli of Nb. Further investigation shows that thermo-electrons have an important role on these anomalies. This effect has not been noticed before. With increased electronic temperature, it is found that all anomalies (both the elastic softening and anisotropy) in Nb are gradually diminished, effectively giving rise to a temperature-induced hardening phenomenon.