Synthesis and thermal expansion of chalcogenide MAX phase Hf2SeC

Thermal expansion of MAX phases along different directions tends to be different because of the anisotropy of hexagonal crystals. Herein, a new Hf2SeC phase was synthesized and confirmed to be relatively isotropic, and the coefficients of thermal expansion (CTEs) along a and c directions were determined to be 9.73 μK−1 and 10.18 μK−1, respectively. The strong MS bond endowed Hf2SC and Zr2SC lower CTEs than those of Hf2SeC and Zr2SeC. The relationship between the thermal expansion anisotropy and the ratio of elastic stiffness constant c11 and c33 was established. This straightforward approximation can be used to roughly predict the thermal expansion anisotropy of MAX phases.