Synthesis, doping and electrical bulk response of (Bi1/2Na1/2)xBa1-xTiO3Â + CaO -based ceramics with positive temperature coefficient of resistivity (PTCR)

(Bi1/2Na1/2)xBa1-xTiO3 samples were prepared using the mixed-oxide route; their tetragonal to cubic phase transition temperature increases from 125 °C for x = 0-190 °C for x = 0.2. (Bi1/2Na1/2)0.10Ba0.90TiO3 (x = 0.10) ceramics with CaO addition sintered in air exhibit a positive temperature coefficient of resistivity (PTCR) behavior. Dense PTCR thermistor ceramics with low room-temperature resistivity and resistivity change ρmax/ρmin of 3.5 orders of magnitude at the Curie temperature were prepared using 3.5 mol% CaO, 0.05 wt% SiO2 addition as sintering aid, and Mn+Fe acceptor doping. Sintering at 1235 °C with two hours holding time were found as optimum synthesis conditions for achieving a good electrical thermistor performance. Impedance spectroscopy confirms that the resistance change is a grain boundary phenomenon, since the grain interior exhibits semiconducting behavior across the phase transition.