| BaTiO3（BT）-based positive temperature coefficient of resistivity （PTCR）ceramics were prepared by solid state reaction and sol-gel methods. All ceramicsamples were sintered in air atmosphere. With an increase of (Bi0.5Na0.5)TiO3（BNT）content, the Curie temperature could be improved rapidly, but the room temperatureresistivity also increased.When the addition of BNT exceed1mol%, the samples could not besemiconducting in air sintering by solid-state reaction. Appropriate extra Nb2O5dopedin the start raw materials could offset Bi2O3volatilization and neutralize the redundantacceptor Na+ions. When the extra Nb2O5content is0.6mg, the sampleroom-temperature resistivity is6.3×103Ω·cm, with the Curie point about135℃andthe high PTCR effect of3orders of magnitude. But other ceramic samplescontaining over or less than0.6mg Nb2O5display dielectric properties. When thecontent of BNT=1.5mol%, the BT-BNT ceramics could not transformed tosemiconductor by extra Nb2O5doping. The ceramics could be semiconducting whengraphite was added into raw materials. But with an increase of BNT, the content ofgraphite increases, and the porosity of the BT-BNT ceramics also increases.When the lead free PTCR ceramics were prepared by sol-gel processes, thehigher purity, smaller particle size and more homogeneous powders were obtained,which were effective in lower synthesis temperature. When the addition of BNT was5mol%, the samples could be semiconducting by air sintering. The sampleroom-temperature resistivity was4.46′106Ω·cm, with the Curie temperature about148℃and the high PTCR effect of2orders of magnitude. However, with>5mol%BNT addition, the BT-BNT ceramics transformed to an insulator.The effect of different BNT contents on phase composition, lattice parameters,microstructure and PTC property of samples was investigated. With an increase ofBNT content, all samples showed single perovskite phase, but the lattice parameters,the size of grain and the jump of resistivity decreased. |
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