Superconducting Sn-Intercalated TaSe$_2$: Structural Diversity Obscured by Conventional Characterization Techniques

Abstract: Using Sn-intercalated TaSe$2$ as a model system, we uncover structural heterogeneity by single-crystal X-ray diffraction that eludes the common characterization techniques of powder X-ray diffraction, Raman spectroscopy, and electrical transport measurements. From a single growth composition (1:1:2 Sn:Ta:Se), we obtain diverse stoichiometries and structures, with near-continuous intercalation for Sn$_x$TaSe$_2$ from $0\leq\textrm{x}\leq1$. Using single-crystal X-ray diffraction, we identify four new structures: Sn${0.18}$TaSe${1.92}$ ($R3m$), Sn${0.37}$TaSe${2.14}$ ($R\bar3$), Sn${0.42}$TaSe${2.04}$ ($P\bar31c$), and Sn${1.1}$TaSe$_2$ ($Fmm2$). In contrast, powder X-ray diffraction cannot resolve all four structures. Raman spectroscopy is unable to distinguish different structures or compositions in the standard measurement range. Transport measurements show consistent superconductivity irrespective of Sn-intercalation amount or appearance of charge density wave behavior. This work underscores the inadequate sensitivity of common approaches in capturing the structural diversity of intercalated transition metal dichalcogenides and the need for high-resolution structural characterization when examining the properties of van der Waals-layered compounds.