Metastable MoS2 : Crystal Structure, Electronic Band Structure, Synthetic Approach and Intriguing Physical Properties.

The 2H molybdenum disulfide (MoS2 ), as a stable hexagonal phase, has been one of the most studied transition metal dichalcogenides over the past decades. In the last five years, the metastable phases of MoS2 (1T, 1T', 1T'', and 1T''') have seen a revival of interests. Different from the edge-sharing [MoS6 ] trigonal prisms in the 2H MoS2 phase, these metastable phases are composed of the edge-sharing [MoS6 ] octahedra, in which the neighboring Mo-Mo distances differ. Due to the various crystal structures and different electronic configurations of the building [MoS6 ] motifs, these metastable polytypes are endowed with intriguing physical properties and potential applications in diverse fields. In this Review, the recent research progress on metastable MoS2 is summarized, especially with an emphasis on the diverse synthetic approaches and the newly uncovered physical properties. The phase structures and electronic band structures are also outlined. In the end, a perspective of the future investigation on metastable MoS2 is discussed.