Effects Of Acceptor Oxide Dopants On Electrical Properties And Microstructure In BaTiO₃-Based PTC Ceramics

Three series of BaTiO3-based PTC ceramics samples have been prepared by solid state reaction method under the same sintering regime through the following doping ways:firstly, BaTiO3are doped with0.3%mol of Y2O3as a donor dopant, and then they are doped with different contents of MnO2, CuO and Fe2O3as acceptor dopants, respectively. The effects of acceptor oxide dopants on electrical properties and microstructures in the BaTiO3-based PTC ceramics samples have been studied by the measurements of positron annihilation spectra and electrical properties. The results are as follows:(1) The variations of the electrical properties of the three series of BaTiO3-based PTC ceramics samples with the increasing of the content of acceptors are quite similar, that is, the room temperature resistivity ρ25of the samples increases monotonously with the content of acceptors, while the value of ρmax/ρmin increases first and decreases later with the increase of the content of acceptors.(2) The PTC effect of BaTiO3-based ceramics is remarkably enhanced by MnO2doping in comparison with the non-acceptor-doped sample, and the value of ρmax/ρmin of the sample with0.03%mol MnO2is28times to the sample without MnO2.(3) The PTC effect of BaTiO3-based ceramics is also enhanced by CuO doping in comparison with the non-acceptor-doped sample, and the value of ρmax/ρmin of the sample with CuO dopant is ten times higher than the no-acceptor-doped sample. The effects of CuO doping is not as good as MnO2doping in the improvement of PTC property.(4) The effect of Fe2O3dopant on the incresing of the value of the ρmax/ρmin of the BaTiO3-based ceramics is the worst in comparison with the samples doped with MnO2or CuO. The room temperature resistivity ρ25of the samples increases rapidly with the content of Fe2O3dopant.(5) As the content of acceptors are overabundance in the BaTiO3-based ceramics samples, the room temperature resistivity ρ25of the samples increase increases remarkably, while the PTC property of the samples have deteriorated sharply.(6) The variations of the positron lifetime parameters of the three series of BaTiO3-based PTC ceramics samples with the increasing of the content of acceptors are quite similar, that is, the positron lifetimes both in the bulk states and defect states of the BaTiO3-based ceramics doped with acceptors are decreased, while the intensities of positron annihilates in defect states of these samples are increased in comparison with the non-acceptor-doped samples. The results suggest that resistance in the grain decreases due to acceptor doping, while the resistance between the grain boundaries increases because of the increasing of the concentration of defects, which leads to the increase of the value of ρ25and the variation of the values of ρmax/ρmin. As the content of acceptor is overabundance, the positron lifetime and the value of ρ25of the samples increases sharply.