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Nanostructured nickel sulfides synthesized by modified polyol method exhibiting blocking/freezing temperature

2018; Elsevier BV; Volume: 768; Linguagem: Inglês

10.1016/j.jallcom.2018.07.291

1873-4669

Victor Alexandre Veit Schmachtenberg, Gustavo Tontini, Guilherme Dalla Lana Semione, V. Drago,

Quantum Dots Synthesis And Properties

Nickel sulfides show a great variety of thermodynamic stable phases such as Ni3S2, h-Ni7S6, Ni9S8, h-NiS, r-NiS, Ni3S4 and NiS2. Moreover, the hexagonal h-NiS crystalline phase has been academically studied due to a first-order-paramagnetic-antiferromagnetic, metallic-semiconducting transition, both at 265 K and very sensitive to structural or compositional changes. In addition, nanostructured materials have been studied due to their unique properties with no counterpart from the related bulk material. In this context, this study produced nanostructured nickel sulfides in powder form, in particular the hexagonal h-NiS phase (pointed by X-ray diffraction), employing the polyol method, by which the chemical reagents were dispersed (nickel acetate and thiourea) into ethylene glycol under agitation at 190 °C up to 12 h. Electron microscopy shows nanoparticles with polycrystalline nature when comparing the average particle size with the crystallite size obtained by X-ray diffraction. Magnetic measurements between 2 K and 300 K showed paramagnetic behavior at ambient temperature and a blocking/freezing temperature, below which coercivity arises. This might be due to the uncompensated spins of the antiferromagnetic state of the h-NiS phase.