Effect of pressure on structural, elastic and mechanical properties of transition metal hydrides Mg7TMH16 (TM = Sc, Ti, V, Y, Zr and Nb): First-principles investigation

Abstract

The effect of pressure on structural stability, elastic properties and Debye temperature of face centered cubic Mg7TMH16 (TM = Sc, Ti, V, Y, Zr and Nb) hydrides, was investigated by first-principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). The obtained equilibrium lattice parameters and elastic properties at zero pressure for MgH2 and Mg7TMH16 hydrides, are in good agreement with other experimental and theoretical values. The calculations of the bulk modulus and the ductility factors (B/G) show that mixing (MgH2) with small amount of transition metal (TM = Sc, Ti, V, Y, Zr and Nb) can enhance the resistance to volume change and transform it from a brittle to a ductile material (brittle → ductile). The elastic constants, bulk modulus, shear modulus, Young's modulus, anisotropy factor and hardness have been studied under pressure. These mechanical quantities are found to increase with increasing pressure. While the B/G and Poisson's ratios (v) undergo an inverse behaviour. In addition to that, the studied hydrides are found stable with a ductile behaviour under a pressure between 0 and 20 GPa. Furthermore, the effect of pressure on Debye temperature and sound velocity, was also investigated and discussed.