Shape Control and Characterization of Transition Metal Diselenides MSe₂(M = Ni, Co, Fe) Prepared by a Solvothermal-Reduction Process

Transition metal diselenides (MSe 2, M=Ni, Co, Fe) were synthesized successfully through a simple solvothermal-reduction reaction at low temperatures. EDXA and XPS techniques confirmed that the compositions of these diselenides were in good agreement with their stoichiometries. With increasing temperature, the obtained NiSe 2 transformed from initial filament nanocrystallites to final octahedral crystals. The studies on the thermal stability of the as-prepared NiSe 2 showed that NiSe acted in an intermediate role in the pyrolysis process. The Raman spectrum of NiSe 2 presented the peak of the Se−Se stretching mode at 216.5 cm - 1 . XRPD techniques revealed that the as-prepared CoSe 2 at higher temperature had an orthorhombic structure similar to that of FeSe 2 . At low temperature this orthorhombic phase CoSe 2, which displayed rodlike shape with the growth direction along 〈121〉, coexisted with a trace of the cubic phase CoSe 2 .