Electronic structure and mechanical properties of ternary ZrTaN alloys studied by ab initio calculations and thin-film growth experiments

The structure, phase stability, and mechanical properties of ternary alloys of the Zr-Ta-N system are investigated by combining thin-film growth and ab initio calculations. Zr sub(1-z) Ta sub(x) N films with 0 < or - x < or - 1 were deposited by reactive magnetron cosputtering in Ar + N sub(2) plasma discharge and their structural properties characterized by x-ray diffraction. We considered both ordered and disordered alloys, using supercells and special quasirandom structure approaches, to account for different possible metal atom distributions on the cation sublattice. These calculated values are compared with experimental data from thin-film measurements using Brillouin light scattering and nanoindentation tests. We also study the validity of Vegard's empirical rule and the effect of growth-dependent stresses on the lattice parameter. Our findings demonstrate that Zr sub(1-x) Ta sub(x) N alloys with Ta fraction 0.51[< or =, slanted]x[< or =, slanted]0.78 exhibit enhanced toughness, while retaining high hardness ~30 G Pa, as a result of increased valence electron concentration and phase stability tuning.