Superconducting Sn-Intercalated TaSe2: Structural Diversity Obscured by Routine Characterization Techniques

TL;DR

This paper shows that routine methods miss structural diversity in Sn-intercalated TaSe2, requiring advanced techniques for accurate characterization.

Contribution

The study reveals new structure types in Sn-intercalated TaSe2 and highlights limitations of standard characterization techniques.

Findings

Three new structure types were identified using SCXRD and STEM.

Routine methods like powder XRD and Raman spectroscopy failed to detect structural diversity.

Superconductivity and charge density wave behavior remained consistent despite structural variations.

Abstract

Using Sn-intercalated TaSe2 as a model system,
we demonstrate
the presence of structural heterogeneity captured by single-crystal
X-ray diffraction (SCXRD) and scanning transmission electron microscopy
(STEM) that eludes the routine characterization techniques of powder
X-ray diffraction, Raman spectroscopy, and electronic transport measurements.
From a single growth composition (1:1:2 Sn:Ta:Se), we obtained crystals
diverse in stoichiometry and structure, with near-continuous intercalation
for Sn
x
TaSe2 from 0 ≲ x ≲ 1. Using SCXRD, we found global structural diversity,
identifying three new structure types: Sn0.18TaSe2.0/Sn0.08TaSe1.96 (R3m), Sn0.16TaSe2.0 (P63/mmc), and Sn1.2TaSe1.9 (Fmm2). Using STEM, we observed local
structural diversity, manifested as regions of highly variable stacking
within a single crystal. In contrast, powder X-ray diffraction did
not resolve all observed global structures. Raman spectroscopy was
unable to distinguish between different structures or compositions
in the standard measurement range. Electronic transport measurements
showed consistent superconductivity and charge density wave behavior
irrespective of Sn-intercalation amount. Our results indicate that
routine approaches to characterization of intercalated transition
metal dichalcogenides may be inadequate for capturing the diversity
of this family of materials, highlighting the need for high-resolution
structural characterization when examining the properties of van der
Waals-layered compounds.

Figures