Synthesizing Mono- and Bimetallic 2D Selenophosphates Using a P₂Se₅ Reactive Flux

We have developed a new method for synthesizing mono- and bimetallic two-dimensional selenophosphates by using a reactive flux technique with powder precursors dissolved in a P2Se5 melt. This method allows us to bypass the difficulties commonly encountered in synthesizing these materials. M2P2Se6 (M = Mn, Fe, Cr, Cd, Mg, and Zn) and bimetallic MM′P2Se6 (M = Cu, Ag; M′ = Cr, In) powders were synthesized over 60 h using a P2Se5 reactive flux. As a further demonstration of potential optimization, Mn2P2Se6 powder with minor MnSe impurity was synthesized in 30 min. Reactions of Mn and Cr in P2Se5 flux were analyzed in situ using variable-temperature powder X-ray diffraction to investigate the formation reaction pathways, suggesting single-step formation of Cr2P2Se6 at 775 °C and formation of Mn2P2Se6 at 575 °C through an intermediate MnSe phase. Follow-up experimental syntheses generated crystals of the monometallic family M2P2Se6 (M = Mn, Fe, and Cd) and bimetallic family MM′P2Se6 (M = Li, Cu, Ag; M′ = Cr, In) with area dimensions of several square millimeters using heating profiles of just over 60 h. The homogeneity of bimetallic selenophosphates MM′P2Se6 was confirmed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Rietveld refinement. The crystallinity of the selected materials was characterized by transmission electron microscopy and atomic force microscopy measurements. The work functions of flakes were determined and ranged from 5.25 to 5.72 eV.