Preparation,Characterization And Electrical Property Of BaTiO_ 3-based PTC Ceramics Synthesized By Liquid Mixes

As the fundamental raw materials of electronic ceramic components, barium titanate (BaTiO₃) with typical structure of perovskite (ABO₃) has excellent dielectric, piezoelectric, electro-optic and insulation performance. The pure BaTiO₃ ceramic is a kind of excellent insulated materials, whose room temperature resistivity is up to 10¹⁰-10¹²Î©Â·m. In 1950, Haayman et al. found the PTC effect by doping a small amount of rare earth elements in BaTiO₃ ceramics. 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). Since then, the rare earth doped barium titanate ceramics have attracted great interest. A large number of devices based on the PTCR effect and their other properties(R-T,V-I), such as electrical equipments, electrical information, automatic control, biology, resource and so on were produced. we make the PTC effect as our point, donor doping can transfer the insulating barium titanate to semiconductor, and enable it to get low room temperature resistance. Meanwhile, the introduction of acceptor will enhance the grain boundary potential barrier of PTC ceramics, which would increase the resistance jump, finally leading to good PTC effect.In our present work, Ba(OH)2·8H₂O,TiCl₄,Sr(OH)₂·8H₂O,NH₃·H₂O were selected as the raw materials while the Y³⁺,Nd³⁺,Nb⁵⁺ and Mn²⁺ were selected as donor and acceptor ions to be doped into BaTiO₃ host via solid state reaction at low temperature. The Al2O₃, SiO₂, TiO₂ (AST) were used as sintering assistant reagents. The proposed synthesis technique possesses advantages of simple operation craft, time-saving, low energy consumption, non-pollution etc. during the preparation process. This method can also reduce the powder reunion and the nonuniformity which are caused by the intermediate steps and the high temperature sintering. Additional, the semi-conductive degree of the material was also improved with the help of sintering assistant reagents at lower sintering temperature The XRD patterns demonstrated the compounds to be mutually miscible in the solid solutions and 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.Transmission electron microscopy (TEM) showed the samples to consist of uniform, substantially spherical particles with an average particle size of 40-60 nm. Moreover, the doping concentration of the donor and the acceptor, the sintering conditions have been investigated in detail. When the doping concentration of Nb and Mn are 0.32mol% and 0.04mol% respectively, the room-temperature resistance of the sample is 29.6Ω, ratio of lg (Rmax/Rmin) is 5.1 and temperature coefficient of resistanceαis 19.3 %/ oC,while the doping concentration of Y,Nb and Mn are 0.2mol%, 0.18mol% and 0.04mol% respectively, the room-temperature resistance of the sample is 17.6Ω, Rmax/Rmin is 6.5×104 and temperature coefficient of resistanceαis 18.6 %/ oC, the doping concentration of Nd, Nb and Mn are 0.32mol%, 0.28mol% and 0.04mol% respectively, the room-temperature resistance of the sample is 28.7Ω, Rmax/Rmin is 2.3×105 and temperature coefficient of resistanceαis 19.8 %/ oC.In our article, the sintering conditions (sintering temperature, soaking time) has been discussed , oxidation atmosphere sintering condition has been choosen. Through the test of the PTC effect of the materials, the sintering conditions were modified. Compared with the oxidation atmosphere ,the materials showed no effec under C deoxidize conditions.