Study On Low Temperature Sintering Properties Of (Ba, Sr)TiO₃ Semiconducting Ceramics

Since the effect of positive temperature coefficient of resistivity(PTCR) for BaTiO₃ semiconducting ceramics was discovered in 1950s,the PTCR thermistors based on BaTiO₃ semiconductive ceramics materials become the third application behind capacitors and piezoelectric ceramic applications and are used widely in communication,household electrical appliances and automobiles sand.However,conventional BaTiO₃ ceramic is prepared at high sintering temperature above 1300℃.It is rather difficult to realize co-firing process in fabrication of multilayer PTCR devices.To prepare the multilayer components,the low-temperature sintering technology is very important.In this paper,the BaTiO₃ based PTCR ceramics are used as main materials.The aim of this work is to decrease the sintering temperature.PTCR ceramics have been prepared by the conventional solid-state reaction and sol-gel process,a series of works have been done in our study to decrease the sintering temperature.In order to improve PTCR effect of the ceramics sintered at low temperature,the sintering aids and modified sintering aids are added simultaneity.The BaTiO₃ based PTCR ceramics are prepared by conventional solid-state reaction. The BaB₂O₄ sintering aid is synthesized at 1100℃using BaCO₃ and H₃BO₃ powder.The effect of BaB₂O₄ sintering aid on the microstructure,sintering characters and electric properties of the BaTiO₃ based PTCR ceramics are studied.The results indicates that a semiconducting BaTiO₃ ceramic with PTCR effect has been obtained at low temperature by adding BaB₂O₄ as sintering aid and proper amount of BaB₂O₄ addition helps to promoting low temperature sintering of BaTiO₃ ceramics.To decrease the resistivity of PTCR ceramics,the SiO₂ is added in BaO-B₂O₃(BaB₂O₄) and the effects of BaO-B₂O₃-SiO₂ sintering aid on microstructures and PTCR characteristics of BaTiO₃ ceramics are investigated.The results indicate that PTCR ceramics with BaO-B₂O₃-SiO₂ sintering aid adding 5 mol%SiO₂ result in the room-temperature resistivity of 210Ω·cm and a resistivity jump about 10³ when sintered at 1050℃for 3 h. In order to enhance the PTCR effect of BaTiO₃ ceramics sintered at low temperature, Mn is added as acceptor in BaO-B₂O₃-SiO₂ sintering aid.The effects of BaO-B₂O₃-SiO₂-MnO sintering aid on microstructures and PTCR characteristics of BaTiO₃ ceramics were investigated.The result indicates that BaO-B₂O₃-SiO₂-MnO₂ sintering aid with 0.06 mol%Mn content can provide the room-temperature resistivity 306Ω·cm and resistivity jump 4.23×10³.The BaTiO₃ nano powder has been synthesized by sol-gel method.The effects of BaB₂O₄ sintering aid on microstructures and PTCR characteristics of nano-BaTiO₃ ceramics have been investigated.The results indicate that nano-BaTiO₃ ceramics have high sintering activities and uniform compositions.A semiconducting BaTiO₃ ceramic with PTCR effect has been obtained at 1050℃,the room-temperature resistivity 160Ω·cm and resistivity jump 1.45×10⁴.