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.