Structural transitions of ternary imide Li2Mg(NH)2 for hydrogen storage

Phase transitions and energetic properties of Li2Mg(NH)(2) with different crystal structures are investigated by experiments and first-principles calculations. The Li2Mg(NH)(2) with the primitive cubic and orthorhombic structure is obtained by dynamically dehydrogenating a Mg(NH2)(2)-2LiH mixture up to 280 degrees C under an initial vacuum and 9.0 bars H-2, respectively. It is found that the obtained orthorhombic Li2Mg(NH)(2) is converted to a primitive cubic structure as the dehydrogenation temperature is further increased to 400 degrees C or performed by a 36 h of high-energetic ball milling. Moreover, the primitive cubic phase can be converted to an orthorhombic phase after heating at 280 degrees C under 9.0 bars H-2 for 1 h. Thermodynamic calculations show that the orthorhombic phase is the ground state structure of Li2Mg(NH)(2). The mechanism for phase transitions of Li2Mg(NH)(2) is also discussed from the angle of energy. (C) 2014 AIP Publishing LLC.