Abstract:

Ultrafine BaTiO₃-based powders used for making positive temperature coefficient of resistance (PTCR) were synthesized by two
chemical steps: polyacrylamide gel process and liquid phase coating process. Firstly, doped BaTiO₃-based powders were synthesized by
polyacrylamide gel process at rather low temperature, and the physical and chemical characteristics of the gels and the precursor powders were
investigated by DSC, TG, XRD, TEM. The results showed that single phase of (Ba, Sr)TiO₃ was obtained when the gel was calcined at 700℃
for 2h, and the mean diameter of grains d₅₀ was 1.155μm. Secondly, acceptor and sintering aid were coated by an aqueous solution containing
acceptor and additive. The microstructure characterization and sintering behavior of the PTCR powders and PTC effect of the ceramic samples derived
from the PTCR powders were investigated. Ceramic samples with low room temperature resistance 17.5Ω, ratio of the maximum resistivity
to the minimum (R_max/R_min) 10⁴ and temperature coefficient of resistivity (α) 12% were obtained.

Key words: polyacrylamide gel process, liquid phase coating process, BaTiO3-based PTCR powders