A comparative study on positive temperature coefficient effect of BaTiO3–K0.5Bi0.5TiO3 ceramics by conventional and microwave sintering

As a promising material for lead-free positive temperature coefficient of resistivity (PTCR) ceramics, (1−x)BaTiO3–xK0.5Bi0.5TiO3 (x=0.002–0.008) samples were prepared by conventional sintering (CS) and microwave sintering (MS) techniques. The effects of different sintering method on the phase composition, microstructure and PTCR characteristics of the ceramics were investigated. The sintering cycle of ceramics was 2.5 h by MS, whereas it took 14 h by CS. Using the microwave heating, the sintering temperature to get high dense material is lowered by 40 °C compared to CS samples. The XRD results showed that all samples were pure tetragonal phases by both sintering process. Meanwhile, the MS samples had smaller grain size and uniform grain distribution. For PTC ceramics, MS was superior to CS due to rapid processing and uniform temperature distribution throughout the specimen. Thus, it exhibited improved PTC properties with lower room temperature resistivity (ρRT), higher Curie temperature (Tc) and steep resistance jump (lg(ρmax/ρmin)).