Doping effect of Ta 5+ ions on microstructure and electrical properties of BaTiO 3 –(Bi 0.5 Na 0.5 )TiO 3 ceramics with positive temperature coefficient of resistivity

Lead-free 0.912Ba 0.97 TiO 3 –0.088(Bi 0.5 Na 0.5 )TiO 3 – x Ta 2 O 5 (0 ≤ x ≤ 0.005) ceramics with positive temperature coefficient of resistivity (PTCR) were prepared by solid reaction sintering of high-purity metal oxides and carbonates reagents. The doping effect of Ta 5+ ions on the microstructure and electrical properties of the samples was investigated. X-ray diffraction analysis indicated that all the samples were of a single tetragonal perovskite structure with the calculated c / a value first increased and then decreased with increasing x . The Raman shift at 305 cm −1 became strong firstly and then declined, and the broad band at 722 cm −1 narrowed initially and then broadened with the increase in Ta 5+ content. The Curie temperature raised first and then decreased, presenting the highest value up to 170 °C for the samples with x = 0.001. Moreover, after the incorporation of Ta 5+ ions, the PTCR (defined by the resistivity jump with the ratio of maximum to minimum ones) decreased first and then increased, presenting the best PTCR performance for the samples with x = 0.005. And with increasing x , the room temperature resistivity decreased first and then increased, displaying the lowest room temperature resistivity for the samples with x = 0.003.