NaW2S4 and RbxWS2: Alternative Sources for 2M-WS2 and 1T'-WS2 Monolayers.

Abstract

With the recent strive to develop novel quantum materials, including two-dimensional nanosheets, alkali-layered intercalated materials have found a new purpose as starting materials for such compounds. Enriching the library of alkali materials, we present a solid-state synthesis for preparing NaW2S4 (P1̅, No. 2) and RbxWS2 (C2/m, No. 12). Solving their crystal structure from their powder X-ray diffraction patterns, we show that both materials are layered, the former being a slightly distorted version of the latter. We compare the two structures and find that the main difference is the interlayer spacing in the a-direction. We further show that, like their cousin, KxWS2, both compounds can be deintercalated with dilute acid to form superconducting 2M-WS2, with structural and property characterization showing similar behavior, regardless of the starting material. Lastly, we find that both materials can be exfoliated in the same manner as KxWS2 to form superconducting 1T'-WS2 monolayers. We describe an easy one-step method for preparing two new layered materials and, thus, provide more opportunities to access valuable superconducting materials.