Effect of hydrogen concentration on various properties of gamma TiAl

First principles calculation reveals that the TiAlH phases become relatively less stable after the addition of more H atoms, and that the H migration from tetrahedral interstitial site to octahedral site in gamma TiAl should be much easier than that between octahedral sites. Calculation also shows that H concentration has an important effect on mechanical properties of TiAlH phases, and that the energetically favorable TiAlH phase should possess bigger E, G, and G/B values as well as lower elastic anisotropy. Moreover, it is found that the heat capacities of TiAlH phases increase with the increase of H concentration, and that the coefficients of thermal expansion of TiAl and TiAlH phases decrease with the increase of pressure.