The effect of stoichiometry on the structural, thermal and electronic properties of thermally decomposed nickel oxide.

A thermal decomposition route with different sintering temperatures was employed to prepare non-stoichiometric nickel oxide (Ni O) from Ni(NO)·6HO as a precursor. The non-stoichiometry of samples was then studied chemically by iodometric titration, wherein the concentration of Ni determined by chemical analysis, which is increasing with increasing excess of oxygen or reducing the sintering temperature from the stoichiometric NiO; it decreases as sintering temperature increases. These results were corroborated by the excess oxygen obtained from the thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) techniques indicate the crystalline nature, Ni-O bond vibrations and cubic structural phase of Ni O. The change in oxidation state of nickel from Ni to Ni were seen in the X-ray photoelectron spectroscopy (XPS) analysis and found to be completely saturated in Ni as the sintering temperature reaches 700 °C. This analysis accounts for the implication of non-stoichiometric on the magnetization data, which indicate a shift in antiferromagnetic ordering temperature ( ) due to associated increased magnetic disorder. A sharp transition in the specific heat capacity at and a shift towards lower temperature are also evidenced with respect to the non-stoichiometry of the system.