The composite oxide additive containing Mn, Ni, Cr and Co elements for the ZnO varistor was successfully synthesized through the low-temperature combustion synthesis approach. The combustion reaction was carried out using nitrate mixtures of Mn, Ni, Cr and Co as oxidants and hydrazine as fuel. Herein, hydrazine acts as a bidentate bridge ligand, and it forms a complex with metal nitrate. Controlling the pH value of reactant solution by adding the hydrazine had a considerable effect on the combustion characteristics of the precursor and the final synthesized powder properties. The results of the XRD, FT-IR, SEM and TEM analysis indicated that the suitable pH value for synthesizing the composite additive powder with fine grain size and good crystallinity was 7. The precursor prepared at pH=7 exhibited steady and slow combustion characteristics, and its yield rate achieved ca. 100%. With this method, the composite additive fine powder suitable for improvement of the electrical characteristics of ZnO varistor can be synthesized simultaneously on a large scale.
