Using an effective one-dimensional cluster expansion in combination with first-principles electronic structure calculations we have studied the energetics and electronic properties of Sb-Te layered systems. For a Te concentration between 0 and 60 at. $\%$ an almost continuous series of metastable structures is obtained consisting of consecutive Sb bilayers next to consecutive Sb${}_2$Te${}_3$ units, with the general formula (Sb${}_2$)${}_n$(Sb${}_2$Te${}_3$)${}_m$ ($n,m=1,2,...$). Between 60 and 100 at. $\%$ no stable structures are found. We account explicitly for the weak van der Waals bonding between Sb bilayers and Sb${}_2$Te${}_3$ units by using a recently developed functional, which strongly improves the interlayer bonding distances. At $T=0$ K, no evidence is found for the existence of two separate single-phase regions $\delta$ and $\gamma$ and a two-phase region $\delta +\gamma$. Metastable compounds with a Te concentration between 0 and 40 at. $\%$ are semimetallic, whereas compounds with a Te concentration between 50 and 60 at. $\%$ are semiconducting. Compounds with an odd number of Sb layers are metallic and have a much higher formation energy than those with an even number of consecutive Sb layers, thereby favoring the formation of Sb bilayers.

• Received 30 August 2011

DOI:https://doi.org/10.1103/PhysRevB.85.144114