Discovery of Ag_xTaS₂ superconductor with stage-3 structure

Abstract

Through interfacial engineering, such as ion intercalation, we can tune the properties and optimize the performance of transition metal dichalcogenides and their devices. In this study, we present the first-time experimental investigations of stage 3 of AgxTaS2 single crystal, and its superconductivity was discovered at 3.8 K. Highly crystalline stage 1 and 2 were prepared by a proton-driven ion-introduction method. A simple water-soaking process was employed to achieve the stage-3 structure by deintercalation of Ag ions from lower stage structures. Besides, we developed a general stacking rule to determine the crystal structure, and it can predict any higher-order stage structure of AgxTaS2. The superconducting transition temperature was enhanced from 1.7 K for a stage-2 structure to 3.8 K for a stage-3 structure, which is more than four times that of the pristine TaS2 (0.8 K). This enhancement is attributed to the increase in density of states at the Fermi level, which was calculated by density functional theory. Also, the water-soaking process reconstructs the stage-2 into the stage-3 structure while deteriorating its crystallinity. Such a structural distortion is one of the potential reasons for the suppression of charge density wave in stage-2, resulting in the enhancement of superconductivity despite the structural degradation.

Intercalation on Transition Metal Trichalcogenides via a Quasi‐Amorphous Phase with 1D Order

“…The interactions between Ag ions in TMDs (TiS 2 , TaS 2 , and NbSe 2 ) with the 2D structure were investigated via DFT calculations; it has been reported that these intercalation compounds can be synthesized experimentally. [ 5,7b,21 ] When Ag ions were the farthest away from each other, the most stable state could be obtained in TMDs (Figures S16 and S17b,c,e, Supporting Information). Thus, the attraction between cations in ZrTe 3 is unusual among intercalation compounds.…”

“…However, unlike the 2D layered compounds, structural changes in TMT intercalation compounds cannot be comprehended by the simple expansion of the lattice constant. [ 5 ] Structural analysis is the most challenging issue in treating the TMT intercalation compounds because the intercalation into three‐dimensionally spread van der Waals gaps induces flexible structural changes and reduces the crystallinity. Elucidating the crystal structure of TMT compounds after the intercalation process is one of the critical topics in this family.…”

High-Pressure Diffusion Control: Na Extraction from NaAlB14

“…Furthermore, ion exchange, , introduction, , and extraction are also effective for synthesizing metastable materials. These reactions can be applicable in materials with a large difference in chemical bond strength between constituent elements. , If the diffusion of weakly bonded ions can be controlled while maintaining the basic crystal structure, a metastable phase, which cannot be obtained by simple heat treatment, would be formed, and the electron carrier density would be tuned by modulating the elemental composition .…”

“…Such a deteriorated intergrain contact significantly suppresses the ion diffusion flow. Therefore, the synthesis using anisotropic ion diffusion is effective for materials such as glass that flexibly change shape at high temperatures, − soft layered single crystals stacked by the van der Waals force, ,,, and substances with a structure whose volume hardly changes with ion introduction and extraction like zeolite.…”

“…1 To date, various techniques are being developed for synthesizing thermodynamically metastable materials, such as the quenching treatments from highpressure or high-temperature stable phases, 2 mechanochemical processes, 3 and thin-film fabrication technologies. 4,5 Furthermore, ion exchange, 6,7 introduction, 8,9 and extraction 10 are also effective for synthesizing metastable materials. These reactions can be applicable in materials with a large difference in chemical bond strength between constituent elements.…”