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 ) · M o S 2 − ( X ) · M o T e 2 . 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.