Structural, mechanical and electronic properties of (TaNbHfTiZr)C high entropy carbide under pressure: Ab initio investigation

The structural, mechanical and electronic properties of (TaNbHfTiZr)C high entropy carbide are studied by using density functional theory in conjunction with special quasi-random structures. The proposed lattice constant difference as an empirical criterion for high entropy compounds and mixing enthalpy show the formation of (TaNbHfTiZr)C solid solution. The derived elastic stiffness constants also indicate the mechanical stability of (TaNbHfTiZr)C high entropy carbide. At zero pressure, the calculated elastic mechanics obeys the rule of mixture, whereas Vickers hardness is slightly larger than the average value of constituent binary carbides. The computed elastic parameters show that (TaNbHfTiZr)C is brittle, similar to constituent binary carbides. Under high pressure, the lattice constants decrease slightly, and mechanical properties are improved, even the brittleness-ductility transition takes place. The calculated electronic structures show that covalence in (TaNbHfTiZr)C is relatively weaker than ionic bonding. With increasing pressure, covalence in (TaNbHfTiZr)C decreases while ionicity increases. The present research will be valuable for understanding and designing of high-entropy carbides.