BT-Based Research Of PTCR With Low Room Temperature Resistance And High Tc

Low room temperature resistance and high Tc PTCR ceramics is prepared with raw materials of BaCO₃,SrCO₃,Na₂CO₃,TiO2 and Bi2O₃ using traditional solid synthesis processing. The samples of free-lead with high Tc and low room temperature can be made (1) Different content of Na₂CO₃ and Bi2O₃ is added to the system of (Ba,Sr)TiO₃, from the experiments under the different conditions excellent samples can be made with room temperature resistance rate 50?.cm and increasing resistance rate more 104.From the experiment the property can be changed largely only with a bit of Na₂CO₃ and Bi₂O₃. The key is to improve the Tc. In the experiment the Tc is improved with a good rule because the theory of limited double-solids dissolving. The perovskite structure can be obtain of (Na_0.5Bi_0.5)TiO₃ and (Ba,Sr)TiO₃ and the axes ratio of c/a is improved due to the existence of (Na_0.5Bi_0.5)TiO₃ which has a high c/a. The high c/a lead to a hard transformation from the square ferrous phase to cubic (2) the metal Ni is added to decrease the room temperature resistance because Ni has steady property .With different contents of metal Ni the samples show continuously reducing resistance down. Specially the samples changed to conductors when the content is more 10%(wt). From the experiment we can draw the conclusion that the metal Ni can give high density of electrons and high concentration of electrons with high conducting behavior. In the system of Ni(/Ba_0.92-xSr_0.08Na_0.5xBi_0.5x)TiO₃ the content of Ni is less than other metals which contribute to the low room temperature resistance in previous experiments executed by other peoples. The reason lies in the different system with different raw materials. The Na₂CO₃ and Bi₂O₃ added to the system changes the sintering mechanism and structure In the same time the substance concerning being transformed from place to place give a deeply influence. With the cost of low room temperature resistance the samples demonstrate low increasing ratios from the 104 to 150 or so (3) Based on the experiments mentioned above the process of heating is executed with different temperatures. Thanks to the precedent experiences the process of heating executing improves the low temperature resistance and increasingly resistance ratios. In the conditions of (Ba_0.92-xSr_0.08Na_0.5xBi_0.5x)TiO₃,x=0.8% and metal content of10%(wt),the samples shows dramatically different properties in the resistance and increasingly resistance ratios but little changes of Tc. In order to get good samples after heating the samples pass different stages of heating. In the low temperature the temperature mechanism is more slowly and in the high temperature it increases sharply and experiences a short remaining (4)in order to get good properties of samples, different measurements are taken for example excessive contents of AST,TiO₂,Bi2O₃ and reducing atmosphere. In the processing of testing all the samples are put into the ultrasonic equipment to be cleaned...