Effect of thermal annealing on the properties of nickel sulfide nanostructures: Structural phase transition

This work covers the effects of annealing temperature on crystalline size, surface morphology, optical, structural and paramagnetic properties of NiS and Ni3S4 nanostructures grown through SILAR technique into FNBR matrix. Annealing at low temperature was performed in air and vacuum for 8 h. X-ray diffraction results confirm structural phase transitions (like NiS -> Ni7S6 and Ni3S4 -> Ni9S8) and oxidation processes (by the formation of NiO-SO4-H2O) after thermal annealing of nanocomposites (NCs) in a vacuum and in air, respectively. By EDX spectrum the average Ni: S atomic ratio is approximately 1: 1 for as-prepared NiS, 1:0.89 for NiS annealed in a vacuum and 1: 0.91 for NiS annealed in air.