PS Reactive Flux Method for the Rapid Synthesis of Mono- and Bimetallic 2D Thiophosphates MM'PS.

We report a reactive flux technique using the common reagent PS and metal precursors developed to circumvent the synthetic bottleneck for producing high-quality single- and mixed-metal two-dimensional (2D) thiophosphate materials. For the monometallic compound, MPS (M = Ni, Fe, and Mn), phase-pure materials were quickly synthesized and annealed at 650 °C for 1 h. Crystals of dimensions of several millimeters were grown for some of the metal thiophosphates using optimized heating profiles. The homogeneity of the bimetallic thiophosphates MM'PS (M, M' = Ni, Fe, and Mn) was elucidated using energy-dispersive X-ray spectroscopy and Rietveld refinement. The quality of the selected materials was characterized by transmission electron microscopy and atomic force microscopy measurements. We report two novel bimetallic thiophosphates, MnCoPS and FeCoPS. The NiPS and MnNiPS flux reactions were monitored in situ using variable-temperature powder X-ray diffraction to understand the formation reaction pathways. The phases were directly formed in a single step at approximately 375 °C. The work functions of the semiconducting materials were determined and ranged from 5.28 to 5.72 eV.