Synthesis and thermal expansion of chalcogenide MAX phase Hf2SeC

TL;DR

This study synthesized a new Hf2SeC MAX phase, characterized its near-isotropic thermal expansion properties, and established a predictive relationship between elastic stiffness ratios and thermal expansion anisotropy.

Contribution

It introduces a new Hf2SeC phase and links elastic stiffness ratios to thermal expansion anisotropy in MAX phases.

Findings

Hf2SeC has nearly isotropic thermal expansion coefficients.

Strong M-S bonds result in lower CTEs for Hf2SC and Zr2SC.

Elastic stiffness ratio c11/c33 predicts thermal expansion anisotropy.

Abstract

Thermal expansion of MAX phases along different directions tended to be different because of the anisotropy of hexagonal crystals. Herein, a new Hf2SeC phase was synthesized and confirmed to be relatively isotropic, whose coefficients of thermal expansion (CTEs) were determined to be 9.73 {\mu}K-1 and 10.18 {\mu}K-1 along a and c directions. The strong M-S bond endowed Hf2SC and Zr2SC lower CTEs than Hf2SeC and Zr2SeC. A good relationship between the thermal expansion anisotropy and the ratio of elastic stiffness constant c11 and c33 was established. This straightforward approximation could be used to roughly predict the thermal expansion anisotropy of MAX phases.