Phase stability of three-dimensional bulk and two-dimensional monolayer As1-x Sb x solid solutions from first principles

Abstract

The mixing thermodynamics of both three-dimensional bulk and two-dimensional mono-layered alloys of As_1-x Sb _x as a function of alloy composition and temperature are explored using a first-principles cluster-expansion method, combined with canonical Monte-Carlo simulations. We observe that, for the bulk phase, As_1-x Sb _x alloy can exhibit not only chemical ordering of As and Sb atoms at x = 0.5 to form an ordered compound of AsSb stable upon annealing up to [Formula: see text] K, but also a miscibility gap at 475 K [Formula: see text] T [Formula: see text] 550 K in which two disordered solid solutions of As_1-x Sb _x of different alloy compositions thermodynamically coexist. At T > 550 K, a single-phase solid solution of bulk As_1-x Sb _x is predicted to be stable across the entire composition range. These results clearly explain the existing uncertainties in the alloying behavior of bulk As_1-x Sb _x alloy, as previously reported in the literature, and also found to be in qualitative and quantitative agreement with the experimental observations. Interestingly, the alloying behavior of As_1-x Sb _x is considerably altered, as the dimensionality of the material reduces from the three-dimensional bulk state to the two-dimensional mono-layered state-for example, a single-phase solid solution of monolayer As_1-x Sb _x is predicted to be stable over the whole composition range at T > 250 K. This distinctly highlights an influence of the reduced dimensionality on the alloying behavior of As_1-x Sb _x .