NaW₂S₄ and Rb_<i>x</i>WS₂: 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 (<i>P</i>1̅, No. 2) and Rb_<i>x</i>WS₂ (<i>C</i>2/<i>m</i>, 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_<i>x</i>WS₂, 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_<i>x</i>WS₂ 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.