Elastic and electronic properties of select M2AX phases

TLDR

The study reports low‑temperature specific heat measurements for a set of M₂AX phases, including Ti₂AlC, V₂AlC, V₂AsC, Nb₂SnC, Ti₂AlN, Hf₂InC, Nb₂AlC, and Cr₂AlC. Ab initio calculations and sound‑velocity measurements were used to analyze electronic density of states and elastic properties, revealing that transition‑metal d‑bands dominate N(EF) while the A‑group element has minimal influence. The results show high Debye temperatures, a wide range of N(EF) from ~1.4 to 6 (eV f.u.)⁻¹, and bulk moduli exceeding 100 GPa (≈140 GPa for Ti₂AlN), with theory accurately capturing trends but not exact magnitudes.

Abstract

In this letter we report on the low-temperature specific heat of several M2AX phases: Ti2AlC, V2AlC, V2AsC, Nb2SnC, Ti2AlN, Hf2InC, Nb2AlC, and Cr2AlC. The Debye temperatures are quite high. The density of states at the Fermi level, N(EF) varies from ≈1.4 (eV formula unit)−1 to 6 (eV formula unit)−1. Ab initio calculations show that N(EF) is dictated by the transition metal d–d bands; the A-group element has little effect. We also measured the velocity of sound in V2AlC, V2AsC, Ti2AlC, and Ti2AlN. The average bulk modulus of these materials is over 100 GPa, with a high of ≈140 GPa for Ti2AlN. Our theoretical calculations correctly predict the trend in both the density of states and the bulk modulus, although there is some disagreement in the actual values.