Shape control and characterization of transition metal diselenides MSe2 (M = Ni, Co, Fe) prepared by a solvothermal-reduction process

Transition metal diselenides (MSe2, 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 NiSe2 transformed from initial filament nanocrystallites to final octahedral crystals. The studies on the thermal stability of the as-prepared NiSe2 showed that NiSe acted in an intermediate role in the pyrolysis process. The Raman spectrum of NiSe2 presented the peak of the Se-Se stretching mode at 216.5 cm(-1). XRPD techniques revealed that the as-prepared CoSe2 at higher temperature had an orthorhombic structure similar to that of FeSe2. At low temperature this orthorhombic phase CoSe2, which displayed rodlike shape with the growth direction along < 121 >, coexisted with a trace of the cubic phase CoSe2.