A promising new class of high-entropy ceramics: High-entropy oxycarbides with good oxidation resistance

(Hf 0.25 Zr 0.25 Nb 0.25 Ti 0.25 )(C 0.5 O 0.5 ) high-entropy oxycarbides (HECO-1) with good oxidation resistance, as a promising new class of high-entropy ceramics, were synthesized by a facile carbothermic reduction method for the first time. The results showed that the as-synthesized HECO-1 samples had the single-phase rock-salt structure and high compositional uniformity. Compared to the as-synthesized (Hf 0.25 Zr 0.25 Nb 0.25 Ti 0.25 )C high-entropy carbides, the as-synthesized HECO-1 samples possessed the higher initial oxidation temperature and slower oxidation rate to show the better oxidation resistance, making them the promising applications in extreme environments, which was attributed to their higher oxidation activation energy and Gibbs free energy of oxidation reaction. • The novel high-entropy oxycarbides are synthesized via carbothermal method. • They had the single-phase rock-salt structure and high compositional uniformity. • They are shown to exhibit the good oxidation resistance. • The improvement mechanisms of oxidation resistance were discussed in depth.