Effect of MnO addition on the electrical properties of Nb-doped SrTiO3 varistor

The effect of MnO addition on the microstructure and electrical properties of Nb-doped SrTiO3 varistors was investigated by using scanning electron microscopy, I–V and C–V measurement, complex-capacitance plane analysis, and impedance spectroscopy. It was observed that the grain size and dielectric constant of the ceramics decreased with increasing MnO content. The non-linearity coefficient defining varistor characteristics increased significantly from 5 to 43 as the MnO content increased from 0 to 0.03 mol%. The addition of MnO brought on changes in the grain boundary electronic states: as the MnO content increased, the potential barrier height and the breakdown voltage increased but the charge carrier concentration decreased. This behavior was explained through the effect of Mn ions substituting for Ti sites. The substitutional defect MnTi′′ (or MnTi′), formed in both grain boundary region and grain interior, acts as an electron-trap.