Anharmonic effects in the A15 compounds induced by sublattice distortions

TL;DR

This paper uses first-principles calculations to analyze elastic anomalies and lattice instabilities in A15 compounds, highlighting the role of sublattice relaxation effects in their structural behavior.

Contribution

It reveals that sublattice relaxation effects are crucial for understanding the elastic anomalies and instabilities in A15 compounds through first-principles calculations.

Findings

V3Si, V3Ge, and Nb3Sn are intrinsically unstable against certain shear distortions.

Zone center phonons are unstable or very soft in these compounds.

Sublattice relaxation effects are key to explaining their behavior.

Abstract

We demonstrate that elastic anomalies and lattice instabilities in the the A15 compounds are describable in terms of first-principles LDA electronic structure calculations. We show that at T=0 V_3Si, V_3Ge, and Nb_3Sn are intrinsically unstable against shears with elastic moduli C_11-C_12 and C_44, and that the zone center phonons, Gamma_2 and Gamma_12, are either unstable or extremely soft. We demonstrate that sublattice relaxation (internal strain) effects are key to understanding the behavior of the A15 materials.