Low Temperature Sintering Of Fine Grain Size BaTiO₃ PTCR Ceramic

To meet the development of electronic devices towards miniaturization,digitalization and multi-function, thermistor and varistor are made in one lamination process as a dual function device. In this way, the as-made device can protect circuits from overvoltage and overcurrent simultaneously and save lots of volume. As Ba TiO3 and ZnO ceramics vary in properties, it is critical that the sintering temperature and atmosphere of the two materials match during the reduction and reoxidation co-fire process when making the dual function devices. So it is rather important to study the low temperature sintering of fine Ba TiO3 PTCR in reducing atmosphere.The performance of BaTiO3-based PTC has much to do with the properties of the initial BaTiO3 powders. Finer BaTiO3 powders can be sintered to fine-grained BaTiO3 ceramics at lower temperature, and the sintered ceramic retains a high PTC effect and a strong withstand voltage with smaller sizes. In this paper, BaTiO3 hydro-thermal powders were used as starting materials and La2O3 powders were added as donor. We studied the effect of calcining temperature, the amount of dopant addition and sintering atmosphere on the performance of PTC.We investigated the influence of calcining temperature from 800 oC to 1000 oC. As the calcining temperature increased, the tetragonal phase of BaTiO3 gradually increased.At the same time, the room temperature resistivity increased before decreasing, the lift-to-drag ratio together increased and the sintering range broadened. At the calcining temperature of 1000 ?, Ba TiO3 ceramic has the best sintering properties and PTC performance. Then we studied Ba/Ti ratio and the amount of La addition from 0.25 to0.55mol% on the electrical performance of PTC. It infested that Ba CO3 would deteriorate the PTC effect; as the content of La increase, the RT resistivity decrease monotonously while the magnitude of PTC first increase and then decrease. We sintered BaTiO3 ceramics in 3%H2-97%N2, 0.5%H2-99.5%N2 and N2 respectively to study the effect ofatmospheres on its electrical properties. The Ba1.001La0.0035TiO3 sample has the best performance with a room temperature resistivity of 69 ??cm and a lift�to-drag ratio of3.92 when calcined at 1000 oC, sintered at 1050 oC in N2 and reoxided in the air.