Synthesis, doping and electrical bulk response of (Bi1/2Na1/2)xBa1-xTiO3 + CaO -based ceramics with positive temperature coefficient of resistivity (PTCR)

(Bi1/2N1/2)(x)Ba1-xTiO3 samples were prepared using the mixed-oxide route; their tetragonal to cubic phase transition temperature increases from 125 degrees C for x= 0-190 degrees C for x= 0.2. (Bi1/2Na1/2)(0.10)Bao(0.90)TiO(3) (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 rho(max)/rho(min) 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 degrees 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. (C) 2018 Elsevier B.V. All rights reserved.