Properties of Alkaline-Earth-Metal Polynitrogen Ternary Materials at High Pressure

We report the formation of cubic and tetragonal BaSrN 3 at 100 GPa using an ab initio structure search method. Pressure ramping to 0 GPa reveals a reaction pressure threshold of 4.92 and 7.23 GPa for the cubic and tetragonal BaSrN 3 , respectively. The cubic phase is stabilized by coulombic interaction between the ions. Meanwhile, tetragonal BaSrN 3 is stabilized through an expansion of the d-orbital in Ba and Sr atoms that is compensated by delocalization of π-electrons in N through reduction of π overlap. Elastic properties analysis suggests that both phases are mechanically stable. The structures also have high melting points as predicted using an empirical model, and all imaginary modes vanishes at about 2000 K. These results have significant implication for the design of cleaner and environmentally friendly high energy density materials.