Persistent Metallicity and Systematic Vacancies in Tellurium-based Quasi-One-Dimensional Chevrel-Type Single Crystals

The coexistence of prominent structural anisotropies with low-dimensional structural units that approach the atomic scale has endowed numerous emergent materials with unusual and, often, sought-after physical properties. Recently, the highly modular class of ternary transition metal Chevrel-type chalcogenides, consisting of infinite quasi-one-dimensional (q-1D) [Mo3Q3]n– (Q = S, Se, or Te) columnar chains with sub-nanometer-thicknesses intercalated with A+ (A = alkali or rare metals) cations, has garnered renewed interest owing to their potential to manifest q-1D metallic character, superconducting behavior, and predicted 1D Dirac Fermionic states. However, because these q-1D crystals tend to form micron-scale polycrystals, it has often been difficult to thoroughly investigate their structure and chemistry, as well as their sought-after emergent properties. In this study, we demonstrate the vapor-phase-assisted synthesis of sizeable and well-defined single crystals of a tellurium-based q-1D Chevrel-like crystal, In2–δMo6Te6, facilitating detailed investigations of its crystal structure and electronic properties. These crystals showed distinct signatures of structural 1D anisotropy and a persistent metallic character down to 1.7 K, despite the prevailing theory that q-1D metals undergo Peierls distortion. Intriguingly, we uniquely found from the combination of experimental single crystal refinements and first-principles calculations that the distinct structure, radius ratios, and composition intrinsically impose a thermodynamically favored fractional vacancy in roughly 1/8 of the cationic In sites. These results highlight the potential for chemical, structural, and physical property modulation in this class of metallic q-1D crystals that display suitable electronic states for next-generation functional devices.