So, It Turns Out Lanthanides Aren’t All the Same: Structural Stability of LnSbxTe2-x-δ Compounds

Abstract

Lanthanide metals, with their open 4f shells, occupy a special place in the heart of material scientists for their textbook-defying chemistry. This led them to many tailored applications in fine technology, from photodetectors to ferromagnetic materials. Still, these applications are limited by the high costs of extraction and separation of such chemically similar elements. A more nuanced understanding of the differences between lanthanides thus promises invaluable economic and scientific advances. Here, I use the two-dimensional lanthanide antimony tellurides, LnSbxTe2-x-δ (Ln = La-Lu; 0 < x < 1; δ = vacancies), as a platform on which to investigate these differences by constructing and analyzing the stability phase diagram of these compounds. Synthesis and characterization were done respectively through Chemical Vapor Transport, and Energy-Dispersive X-Ray Spectroscopy and Powder X-Ray Diffraction. Analysis of the stability boundary was done through support vector machines. Structural stability revealed to rely critically on the ionic radius of the lanthanide — itself predicted by lanthanide contraction. The smaller the Ln3+ ion, the less stable single-phase systems become. I reason this follows from the increasing strain on the Sb square net layer. Te-doping in Sb contents x < 1 might also contribute to phase separation, perhaps due to the slight difference in size and electronegativity between Te and Sb. These findings are supported by the subsequent synthesis and analysis of LayHo1-ySb0.5Te1.5-δ (y < 1), which revealed a tendency for La to incorporate Sb before Ho. To probe these claims, I suggest further experiments with dilanthanide antimony tellurides, Ln[1]Ln[2]SbTe that may help quantify the degree of the strain effect from the heavier, smaller lanthanides. Subtle differences in nearly identical elements have significant practical effects that can direct the investigation of these quantum materials and cheapen the unique devices made from these metals that compose the “backwater” of the periodic table.