Electical Property And Preparation Of BaTiO₃-based PTC Ceramics Synthesized By Liquid Mixes

BaTiO3, as a kind of typical autunite-tiranium mine structure (ABO3) material, which have excellent ferroelectric, piezoelectricity and insulated property, has been widely used in the production of electric components such as ceramic capacitor, hot-sense resistence, and photoelectricity apparatus. PTCR (positive temperature coefficient of resistivity) property is one of the attractive effects of the semiconducting BaTiO3, which shows abrupt change (increase) in electrical resistivity at Curie temperature (Tc). A large number of devices based on the PTCR effect, such as heaters, current limiters and chemical sensors are produced both in the form of a bulk ceramic and film.In this paper, at first, we recited the theory and explaination of the PTC effect. PTC effect is a crystal boundary effect. On the grain boundary, because of the role of defects and impurities in the formation of two-dimensional surface state by the acceptor, these two-dimensional surface state acceptor with the grain within the interaction carrier, to form the grain surface and temperature-related potential barrier, and deficiencies in the areas of ferroelectric have high activation energy, so that the fall of the carrier concentration and barrier height is very small, the thickness of insulation area is relatively small and relatively little resistance, it good interpreted the grain boundary layer capacitors and ferroelectric phase transition between the PTC effect of the performance.In this experiment, the doped with(Y, Nd, Ce etal) BaTiO3 was prepared by solid state reaction at low temperature. XRD analysis showed that the powders synthesized by this method are cubic perovskite structure, and the figures represent the presence of only BaTiO3 peaks in the samples with and without additives. TEM photograph shows that the particles of the compounds are uniform and substantially spherical in shape with an average particle size of 70 nm in diameter. The PTC effect of the materials has been studied by preparing ceramics. The influence of various donors (Ce, Nd, Y) and acceptor (Mn) on properties of PTC materials has been discussed in this article. The resistance at room temperature decreases by doping donor dopant, and the resistance jump increases dramatically by doping Mn. The variations of different donors and acceptors concentration on properties of PTC ceramic materials, such as resistance at room temperature, resistance jump and resistance temperature coefficient, have been studied in detail. It was found that the risistance is near 37.09Ωat room temprature,ratio of 1g (Rmax/Rmin) is 2.957×105 and temperature coefficient of resistance a is 23.36% /℃, when the content of Y and Mn are 1.0 mol% and 0.04 mol% respectively. Compared with the solid doped, the room temperature decreases about 5Ω, which Y and Mn doped by liquid mixwd. By doping double donor Nd and Y, the room-temperature resistance effectively reduces to 23.11Ω. The donor of Ce is easily compensated by acceptor, so the room-temperature resistance is 121.68Ω, ratio of 1g (Rmax/Rmin) is 1.746×104 and temperature coefficient of resistance a is 16.76%/℃-1.In this article, the effect of sintering conditions (sintering temperature, soaking time) has been discussed and explained to some extent in my opinion. By analyzing the C deoxidize atmosphere and oxidation atmosphere sinter, It can be seen that the room-temperature resistance reduces sharply, which were sintered under reducing conditions. Under oxidizing conditions the room-temperature resistance changes tiny, but the resistivity jump and temperature coefficient of resistance a rise notable. The effect of sintering process has been discussed and explained in theory, and the optimal sintering conditions of different system are confirmed.By analysing the advantages and disadvantages of other preparation of BaTiO3-based PTCR ceramic powder methods, we prepared liquid mixes BaTiO3 powder by solid-state reaction at low temperature. This method exhibits many advantages:no need for solvent, high productivity and selectivity, low energy consumption and simple reaction technology.