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

Abstract As a candidate of lead-free positive temperature coefficient of resistivity (PTCR) materials, Ba 0.94 (Bi 0.5 K 0.5 ) 0.06 TiO 3 – x Na 2 Ti 6 O 13 ( 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 Na 2 Ti 6 O 13 -doped Ba 0.94 (Bi 0.5 K 0.5 ) 0.06 TiO 3 ceramics. Scanning electron microscopy observations revealed that the grain size was improved with increasing Na 2 Ti 6 O 13 content. The samples sintered under reducing atmosphere were reoxidized by annealing in air to induce the PTC effect. The PTCR characteristics of Ba 0.94 (Bi 0.5 K 0.5 ) 0.06 TiO 3 ceramics were investigated in terms of Na 2 Ti 6 O 13 content, reoxidation temperature and time. For x ≤0.15% samples, with the increasing Na 2 Ti 6 O 13 content, both the Curie temperature ( T C ) 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 2.27×10 3  Ω cm, the T C about 145.4 °C and a moderate PTC effect of ρ max / ρ min =2.39.