One-step solvothermal synthesis of nickel selenide series: Composition and morphology control

A one-step oleylamine-mediated solvothermal method was reported for the synthesis of nickel selenide series within a short reaction time. The method provided a suitable nucleation and growth environment in a uniform and transparent solution reaction system. Through adjustment of the Ni/Se raw material ratio and reaction temperature, cubic NiSe2, orthorhombic NiSe2, and hexagonal Ni1−xSe (x = 0–0.15) were obtained. In addition, under an excess nickel source (Ni : Se = 2 : 1) and phase change agent, hexagonal NiSe was converted to rhombohedral Ni3Se2, in which the intermediate phase (NiSe) acted as both reactant and template, plus an effect on Ni3Se2 morphology. At a certain reaction temperature of 260 °C, the phase transformation and morphology can be adjusted by changing the solvents (mixture of OLA and ODE). Finally, the conversion mechanism from cubic NiSe2 to orthorhombic NiSe2 at different reaction temperatures was investigated, and the formation process of a nickel selenide series had also been studied through synthetic route controlled experiments. This paper provided a simple and low cost method to control the composition and morphology of nickel selenide series, which would be of great potential for the synthesis of other metal selenides.