Fig. 2.

Co–Sb–(SnTe)_0.5 experimental ternary phase diagram: samples 1–4 are experimentally synthesized and lie along the Co₄Sb₁₂–Co₄–Sn₆Te₆ pseudo-binary highlighted by the black dashed line. The nominal compositions of samples 1, 3 and 4 were chosen based on their potential anion ring ratios. The XRD results in Fig. ES1^† allow us to define our Alkemade lines shown here by the encompassed colored triangles. We see no presence of a quaternary skutterudite in this phase space.