Urea-Melt Assisted Synthesis of Ni/NiO Nanoparticles Exhibiting Structural Disorder and Exchange Bias

Abstract

An easy, inexpensive urea-melt assisted route was designed for the synthesis of ∼10 nm-sized Ni/NiO nanoparticles (NPs). The method consists of the thermal decomposition of a urea-melted medium containing a Ni2+-salt and involves the olygomerization and self-combustion of the organic matrix and the formation of the Ni/NiO NPs within it in a two stepped process of Ni2+ reduction yielding Ni crystallization and subsequent inward oxidation. Control over the microstructural features of the NPs within three typical regimes was accomplished by means of the initial urea quantity. Type A samples (0.2 g urea/0.2908 g nickel nitrate) consists of NiO nanostructures which might contain dispersed Ni nuclei of a few atoms; B NPs (2 g urea/0.2908 g nickel nitrate) are made of proper small Ni cores, in the limit of the coherence length of XRD, surrounded by thick NiO shells, while C (20 g urea/0.2908 g nickel nitrate) NPs correspond to relative big Ni cores and thin NiO shells. Further control over the thickness of the N...