First-Principles Prediction of Stable Transition Metal Dichalcogenide Alloys*

Quasibinary alloying among pairs of 2-dimensional (2D) transition metal dichalcogenides (TMDCs) is an attractive method for tuning properties for applications such as optoelectronics and catalysis. Of the many possible combinations of TMDCs, the small subset of semiconducting alloys have garnered widespread attention. Outside this limited subset, the synthesizability of alloys remains largely unknown. In order to the guide synthesis of such alloys, we present ab initio calculations of equilibrium phase diagrams with regions of stability for 27 TMDC alloys: M_1-x M'_xX₂ and MX_2(1-x) X'_2x (M,M'= V, Nb, Ta, Mo, or W; X,X'= S or Se) and two heterostructural alloys, Mo_1-x W_xTe₂ and WS_2(1-x)Te_2x. We predict four new alloys that are miscible at all temperatures: Nb_1-xTa_xS₂, Nb_1-xTa_xSe₂, VS_2(1-x) Se_2x, and TaS_2(1-x) Se_2x. For the rest of the alloys, we present a qualitative analysis of synthesizability based on miscibility temperatures. We relate TMDC size mismatch with a mixing asymmetry that indicates the synthesizability of low concentration alloys. Our results open new compositional spaces that can be used to design and synthesize TMDC alloys for various applications.