Prediction of entropy stabilized incommensurate phases in the system M o S 2 - M o T e 2

A first principles phase diagram calculation, that included van der Waals interactions, was performed for the 3D bulk system (1-X)·MoS2-(X)·MoTe2. Surprisingly, the predicted phase diagram has at least two ordered phases, at X≈0.46, even though all calculated formation energies are positive; in a ground-state analysis that examined all configurations with 16 or fewer anion sites. The lower-temperature I-phase is predicted to transform to a higher-temperature I′-phase at T≈500 K, and I′ disorders at T≈730 K. Both these transitions are predicted to be first-order, and there are broad two-phase fields on both sides of the ordered regions. Both the I- and I′-phases are predicted to be incommensurate, i.e., aperiodic: I-phase in three dimensions; and I′-phase in two dimensions.