An example of how competing compounds define the stability region of the quaternary material Cu 2 HgGeTe 4 is shown in Figure . By considering only the formation of bulk elemental phases, the stability region of Cu 2 HgGeTe 4 is bounded by ∆µ Cu , ∆µ Hg , ∆µ Ge , ∆µ Te ≤ 0 (Figure ). As competing compounds such as CuTe and Hg 2 GeTe 4 are considered, new facets are introduced as in Equation ( ) until the final phase stability region of Cu 2 HgGeTe 4 emerges (Figure ).