Abstract
0.935Ba<TEX>$TiO_3$</TEX>-0.065(<TEX>$Bi_{0.5}Na_{0.5}$</TEX>)<TEX>$TiO_3+xmol%MnO_2$</TEX> (BBNTM-x) ceramics with <TEX>$0{\leq}x{\leq}0.05$</TEX> were fabricated with muffled sintering by a modified synthesis process. Their microstructure and enhanced positive temperature coefficient of resistivity (PTCR) characteristics were systematically investigated in order to obtain lead-free high TC PTCR thermistors. All specimens showed a perovskite structure with a tetragonal symmetry and no secondary phase was observed. Grain growth was achieved when the doped MnO2 was increased above 0.02 mol%. This is due to the effect of positive Mn ion doping as an acceptor compensating a Ba vacancy occurred by the higher donor dopant concentration of <TEX>$Bi^{3+}$</TEX> ion. Especially, enhanced PTCR characteristics of the extremely low <TEX>${\rho}_{RT}$</TEX> of <TEX>$9\;{\Omega}{\cdot}cm$</TEX>, PTCR jump of <TEX>$5.1{\times}10^3$</TEX>, <TEX>${\alpha}$</TEX> of 15.5%/<TEX>$^{\circ}C$</TEX> and high <TEX>$T_C$</TEX> of <TEX>$167^{\circ}C$</TEX> were achieved for the BBNTM-0.04 ceramics.
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