Effect of Na2Ti6O13 addition on the microstructure and PTCR characteristics of Ba0.94(Bi0.5K0.5)0.06TiO3 ceramics

As a candidate of lead-free positive temperature coefficient of resistivity (PTCR) materials, Ba0.94(Bi0.5K0.5)0.06TiO3–xNa2Ti6O13 (x=0−0.20%) ceramics were prepared by the solid-state reaction technique. X-ray diffraction results indicated that there was no secondary phase detected in the Na2Ti6O13-doped Ba0.94(Bi0.5K0.5)0.06TiO3 ceramics. Scanning electron microscopy observations revealed that the grain size was improved with increasing Na2Ti6O13 content. The samples sintered under reducing atmosphere were reoxidized by annealing in air to induce the PTC effect. The PTCR characteristics of Ba0.94(Bi0.5K0.5)0.06TiO3 ceramics were investigated in terms of Na2Ti6O13 content, reoxidation temperature and time. For x≤0.15% samples, with the increasing Na2Ti6O13 content, both the Curie temperature (TC) and the room temperature resistivity increased. With x=0.15%, the obtained ceramic through a suitable reoxidation process possessed a relatively low room temperature resistivity about 2.27×103Ωcm, the TC about 145.4°C and a moderate PTC effect of ρmax/ρmin=2.39.