First-principles study of structural stability, elastic and electronic properties of ternary rare earth-transition metal—Borides and carbides (RTxZ, R=Sc, Y, and La, T=Pt and Pd, Z=B and C, and x=2, 3, and 4)

Using first-principles total energy calculations (CASTEP code), the structural stability, elastic, and electronic properties of ternary rare earth-transition metal borides and carbides (RTxZ, R=Sc, Y, and La, T=Pt and Pd, Z=B and C, and x=2, 3, and 4) compounds were studied. Results show that RT3Z compounds with tetragonal P4mm structure are energetically more favorable than usually cubic perovskite-type structure. Furthermore, RT3Z with perovskite structure is found to be mechanically unstable with the negative C44. Formation enthalpy calculations indicate that Pt-based borides are easier to be synthesized compared with Pd-based ones and counterpart carbides, respectively. Elastic constants, bulk moduli, shear moduli, Young's moduli, and Poisson's ratio of studied compounds have been calculated. Also, all the studied compounds show ductile behavior. Moreover, total and partial density of states (DOSs) and bonding charge density were employed to elucidate the bonding features of these compounds. The results reveal that the covalency between Pt-5d and Z-2p as well as T-nd (n=4 for Pd and 5 for Pt) and B-2p states, are the cause of the relatively higher elastic moduli of Pt-based compounds and R–T-borides, respectively.