Base metal nickel is often used as the inner electrode in multilayer chip positive temperature coefficient resistance （PTCR）. The fine grain of ceramic powders and base metal nickel are necessary. This paper uses reducing hydrazine to gain submicron nickel powder whose diameter was 200-300 nm through adjusting the consumption of nucleating agent PVP properly. The submicron nickel powder could disperse well and was fit for co--fired of multilayer chip PTCR. It analyes the submicron nickel powder through x-ray Diffraction （XRD） and calculates the diameter of nickel by PDF cards. Using XRD analyses it obtains several conclusions： If the molar ratio of hydrazine hydrate and nickel sulfate is kept to be a constant, when enlarging the molar ratio of NaOH/Ni^2＋, the diameter of nickel powder would become smaller. When the temperature in the experiment raises to 70-80 ℃, nickel powder becomes smaller too. And if the molar ratio of NaOH/Ni2＋ is 4, when molar ratio of （C2H5O）2/Ni^2＋ increases, the diameter of nickel would reduce. Results from viewing the powders by optical microscope should be the fact that the electrode made by submicron nickel powder has a better formation and compactness. Furthermore, the sheet resistance testing shows that the electrode made by submicron nickel is smaller than that made by micron nickel.
The green sheets with Ni paste as inner electrodes were sintered at 1 320 ℃ for 1 h under a N2/H2 mixing gas at an oxygen partial pressure p(O2)=10-8-10-12 MPa, and then reoxided at 900-1 000 ℃ to form multilayer positive temperature coefficient of resistance(PTCR). During the experiments, electronic characteristic effects of PTC with different thicknesses were contrasted. A certain extending of Ni diffusion is beneficial to the ohmic contact of multilayer PTCR but excessive diffusion is harmful to PTCR. The diffusion was studied by scanning electron microscopy(SEM) and energy-dispersive X-ray spectrometry(EDS). Inter-diffusion of element takes place along the Ni-BaTiO3 interface, especially Ni diffusion to BaTiO3 dominated the process. Furthermore, the degree of Ni diffusion is very severe as ceramic layers are very thin.
