中文摘要：

为提高钛酸钡基PTC陶瓷的升阻比（ρmax/ρmin ）,采用固相反应法制备了以Y2 O3为施主杂质,不同含量的MnO2作为受主杂质的钛酸钡基PTC陶瓷样品；应用第一性原理方法计算了样品的能带结构、电子结构和Mn掺杂的形成能；测量了样品的正电子湮没寿命谱和电性能.计算结果表明：钛酸钡材料的价带顶和导带底分别位于特殊K点中X（0,0.5,0）点和Г（0,0,0）点,属间接带隙,禁带宽度为1.59 eV；从形成能结果来看,Mn进入钛酸钡基陶瓷结构后会取代Ti位置.实验结果显示,随着MnO2掺杂量的增加,样品晶粒内部的自由电子密度增大,陶瓷的晶界缺陷浓度增加,室温电阻率增大. MnO2含量为0.03%mol 的样品的升阻比最大,达到1.1×105,即掺入少量的MnO2可明显改善钛酸钡基PTC陶瓷的升阻比.

英文摘要：

In order to increase the values ofρmax/ρmin for the BaTiO3-based PTC ceramics, a series of BaTiO3-based PTC ceramics were prepared by solid state reaction method. The PTC ceramics with Y2 O3 as their donor dopants were doped with different contents of MnO2 as acceptor. The band struc-tures, electronic structures, and the formation energies of the BaTiO3 ceramic samples were calculat-ed by the first-principle method. The positron lifetime spectra and electrical properties of the sam-ples were also measured. The calculation results show that the bottom of valence-band and the top of conduction-band in BaTiO3 are at X（0, 0. 5, 0）point and Г（0, 0, 0） point, respectively; Thus, the BaTiO3 has an indirect gap with the value of 1. 59 eV. The formation energies of the samples＆amp;nbsp;indicate that Ti is replaced by Mn in BaTiO3 . The experimental results show that with the increase of MnO2 content, the electron density in the grain, the concentration of defect of grain boundaries, andρ25 of the ceramics also increase. The ratio ofρmax/ρmin reaches a maximum value （1. 1×105） for the sample doped with 0. 03%mol MnO2 , that is, the ratio ofρmax/ρmin of the BaTiO3-based PTC ce-ramics can be improved by doping small content of MnO2 .