Structural, stability and electronic properties of C15-AB2 (A = Ti, Zr; B = Cr) intermetallic compounds and their hydrides: An ab initio study

Abstract

The structural, stability and electronic properties of C15- AB 2 ( A = Ti , Zr ; B = Cr ) isomeric intermetallic compounds were systematically investigated by using density functional theory (DFT) and plane-wave pseudo-potential (PW-PP) method. The macroscopic properties including the lattice constant, bulk modulus and stability for these compounds were studied before and after hydrogenation. For parent compounds, the enthalpy of formation was evaluated with regard to their bulk modules and electronic structures. After hydrogenation of compounds at different interstitial tetrahedral sites ( A 2 B 2, A 1 B 3, B 4), a volume expansion was found for hydrides. The stability properties of hydrides characterized the A 2 B 2 sites as the site preference of hydrogen atoms for both compounds. The Miedema's "reverse stability" rule is also satisfied in these compounds as lower the enthalpy of formation for the host compound, the more stable the hydride. Analysis of microscopic properties (electronic structures) after hydrogenation at more stable interstitial site ( A 2 B 2) shows that the H atoms interact stronger with the weaker (or non) hydride forming element B   (Cr) than the hydride forming element A  ( Ti/Zr ). A correlation was also found between the stability of the hydrides and their electronic structure: the deeper the hydrogen band, the less stable the hydride.