Synthesis and Stability Phase Diagram of Topological Semimetal Family LnSb_xTe_2-x-δ

The solid solution LnSb_xTe_2-x-δ (Ln = lanthanide) is a family of square-net topological semimetals that exhibit tunable charge density wave (CDW) distortions and band filling dependent on x, offering broad opportunities to examine the interplay of topological electronic states, CDW, and magnetism. While several Ln series have been characterized, gaps in the literature remain, inviting a systematic survey of the remaining composition space that is synthetically accessible. We present our efforts to synthesize LnSb_xTe_2-x-δ across the remaining lanthanides via chemical vapor transport. Compiling our results with the reported literature, we generate a stability phase diagram across the ranges of Ln and x. We find a stability boundary for intermediate x beyond Tb, while x = 1 and x = 0 can be isolated up to Ho and Dy, respectively. SEM and XRD analyses of unsuccessful reactions indicated the formation of several stable binary phases. The presence of structurally related LnTe₃ in samples suggests that stability is limited by the size of Ln, due to increasing compressive strain along the layer stacking axis with decreasing size. Finally, we demonstrate that late Ln can be stabilized in LnSb_xTe_2-x-δ via substitution into larger Ln members, synthesizing La_1-yHo_ySb_xTe_2-x-δ as a proof of concept.