![]() Over the past decades, enormous effort has been dedicated to enhancing the hardness of refractory ceramic materials. ![]() Calculations performed for disordered or ordered structures both lead to the same conclusion regarding the mechanical behavior of these nitride alloys, in agreement with recent literature findings. Our findings demonstrate that Zr1−xTaxN alloys with Ta fraction 0.51⩽x⩽0.78 exhibit enhanced toughness, while retaining high hardness ∼30 GPa, as a result of increased valence electron concentration and phase stability tuning. The thermal stability of these Zr1−xTaxN films is also studied, based on their structural and mechanical response upon vacuum annealing at 850 ☌ for 3 h. We also study the validity of Vegard's empirical rule and the effect of growth-dependent stresses on the lattice parameter. These calculated values are compared with experimental data from thin-film measurements using Brillouin light scattering and nanoindentation tests. Density functional theory within the generalized gradient approximation was employed to calculate the electronic structure as well as predict the evolution of the lattice parameter and key mechanical properties, including single-crystal elastic constants and polycrystalline elastic moduli, of ternary Zr1−xTaxN compounds with cubic rocksalt structure. 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. Zr1−xTaxN films with 0≤x≤1 were deposited by reactive magnetron cosputtering in Ar+N2 plasma discharge and their structural properties characterized by x-ray diffraction. 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. ![]() Utilizing the anisotropic Poisson's ratio to approximate the relaxed transverse lattice parameters at a given axial strain is a good approximation to stress-strain curves, and ideal strengths obtained in this way exhibit strong correlations to experimental Vicker's hardness values. With a view to circumvent the need to run computationally-expensive relaxation steps, different methodologies for approximating uniaxial stress-strain curves are introduced. The isotropic elastic stiffness constants, c_ exhibit stronger correlations. Density functional theory calculations are performed to evaluate the hardness of various cubic metal nitrides: rocksalt TiN, VN, ZrN, NbN, AlN, and SiN zincblende AlN and BN and diamond C for comparison. ![]()
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