To the stability of Janus phases in layered trichalcogenide MPX3 crystals: Insights from experiments and theory

The stability and electronic structure of the possible Janus phase for the representative example of transition metal trichalcogenide FePS_1.5Se_1.5 crystals are studied and discussed. The respective stoichiometric layered parent (FePS₃ and FePSe₃) and mixed (FePS_1.5Se_1.5) compounds are successfully synthesized, and our experimental data confirm the high quality of the obtained crystals and the uniform random distribution of S and Se atoms in the chalcogens’ layers for the FePS_1.5Se_1.5 crystals. These results are supported by the detailed density functional theory calculations, which indicate the absence of the Janus phase for the layered 3D FePS_1.5Se_1.5. This effect is explained by the large uncompensated dipole moment for the Janus phase, and the possible routes for the stabilization of 2D FePS_1.5Se_1.5 Janus layers are discussed.