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 Hf 2 SeC 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 Hf 2 SC and Zr 2 SC lower CTEs than those of Hf 2 SeC and Zr 2 SeC. The relationship between the thermal expansion anisotropy and the ratio of elastic stiffness constant c 11 and c 33 was established. This straightforward approximation can be used to roughly predict the thermal expansion anisotropy of MAX phases.