Preparation And Microstrcture Of BaTiO₃-based PTC Ceramics Synthesized By Liquid Mixes And Its Electrical Propertics

A large number of devices based on the PTCR effect, such as heaters, current limiters andchemical sensors are produced both in the form of a bulk ceramic and film. BaTiO₃, as a kindof typical autunite-tiranium mine structure （ABO3） material, which have excellentferroelectric, piezoelectricity and insulated property, has been widely used in the productionof electric components such as ceramic capacitor, hot-sense resistence, and photoelectricityapparatus. With further research, the PTC material towards direction of high-tech,highperformance. Research and development of high-performance PTC ceramic is hot recently.Such applications require the PTC material has a low resistivity at room temperature, highpressure and withstand the impact of the high current characteristics. Therefore, research ofthe project is a focus of research workers.BaTiO₃ceramics doped with Bi were prepared by liquid mixes and solid-state reaction atlow temperature. The hydrated oxides of titanium and bismuth through hydrolysis of TiCl₄and BiCl₃and calculated amount of Ba（OH）2·8H2O and Sr（OH）2·8H2O were mixed andground in mortar for1h at room temperature. Then the BaTiO₃-based nano-crystallinelenswas obtained. The XRD, TEM and SEM were used to study the phases and micrographs. Theinfluence of sintering process on the electrical properties was studied.The results show thatthe compounds are mutually miscible in the solid solutions and have a shape of uniform,substantially spherical particles with an average partical size of60nm in diameter. It wasfound that the R25is26.29and ratio of Rmax/Rmin is3.585×104respectively when theceramics materials sintered at1330℃for20min.A series of doped BaTiO₃-based PTC ceramic powders used BiCl₃and NbCl₅as donordopant were prepared by solid-state reaction at low temperature. The influence of sinteringprocess on the PTC effect was studied. The XRD and TEM were used to study the phases andmicrographs. The results show that the compounds are mutually miscible in the solidsolutions and have a shape of uniform, substantially spherical particles with an averagepartical size of50⁶0nm in diameter. As indicated by preparing ceramics, the PTC effect is improved by doping double donor Bi and Nb. It was found that the R25is12.93and ratioof Rmax/Rmin is1.920×105respectively when the ceramics materials sintered at1330℃for20min.A series of doped BaTiO₃-based PTC ceramic powders used La and Nb as donor dopantwere prepared by solid-state reaction at low temperature. The XRD and TEM were used tostudy the phases and micrographs. The results show that the compounds are mutually misciblein the solid solutions and have a shape of uniform, substantially spherical particles with anaverage partical size of60⁷0nm in diameter. The effect of sintering conditions （sinteringtemperature, soaking time） has been discussed and explained to some extent in my opinion. Itis found that the room-temperature resistance is36.74, ratio of Rmax/Rmin is1.066×105and the resistance-temperature coefficient is22.78％℃-1, when the ceramicsmaterials sintered at1340℃for20min.The effect of sintering conditions （sintering temperature, soaking time, cooling rate） hasbeen discussed. With the sintering temperature be higher and cooling rate be faster,thesample size shows a trend of decreases and then increases, the R25decreases and thenincreases, and ratio of Rmax/Rmin increases and then decreases.