Alloying Effect Study on Thermodynamic Stability of MgH2 by First-principles Calculation

Abstract

First-principles calculations based on density functional theory were performed to study the effect of alloying on the thermodynamic stability of MgH2 hydride (rutile and fluorite structures) with transitional metals (TM=Sc, Ti, Y) and group IIA elements (M=Ca, Sr, Ba). The results indicate that fluorite structure of these hydrides are more stable than its relative rutile structure at low alloying content (less 20%), structural destabilization of MgH2 appears in the alloying cases of Ti, Sr and Ba respectively. The structure-transition point from rutile structure to fluorite structure is at around 20% for MgH2-TM, and about 40% for MgH2-M. The formation enthalpy of fluorite Mg0.5Ba0.5H2 is about 0.3 eV and higher than that of fluorite MgH2, indicating that its hydrogen-desorption temperature at atmospheric pressure will be much lower than that of pure MgH2. Good consistency between experimental and calculated data suggests that above-adopted method is useful to predict structural transition and properties of MgH2 based hydrides for hydrogen storage.