NaW₂S₄ and Rb_xWS₂: Alternative Sources for 2M-WS₂ and 1T′-WS₂ Monolayers

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 Rb_xWS₂ (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, K_xWS₂, 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 K_xWS₂ 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.