Theoretical insight into structural and mechanical features of Hf0.5Ta0.5C

Tantalum carbide (TaC) and hafnium carbide (HfC), as well as mixed hafnium tantalum carbides, are of great recent scientific and industrial interest due to their structural features, and thermal, elastic, and mechanical properties. In order to identify the possible crystal structure candidates in the Hf0.5Ta0.5C system that are (meta)stable for different pressures, a global search was performed on the energy landscape of the system. The structure candidates obtained were further locally optimized on the DFT level, and the relaxed structures were crystallographically analyzed and compared. As a result, the experimentally observed rock salt phase was found as a global minimum, and an additional dozen feasible modifications of Hf0.5Ta0.5C were predicted. Besides the experimentally observed NaCl-type structure, various distorted versions of this structure type were found, as well as modifications exhibiting the NiAs-, ortho-, and 5-5-type of structure. Furthermore, mechanical properties including bulk, shear, Young’s moduli, elastic constants, and the Vicker´s hardness were computed for all promising predicted structure candidates. We believe that the present results will help in understanding the structure-property relationship in mixed HfC/TaC systems