Electrical phenomena such as positive temperature coefficient of resistance (PTCR), grain boundary layer capacitance, and varistors are controlled by Schottky barriers to current transport formed in grain boundary regions. These grain boundary potential barriers are a result of charged defect accumulation, either through equilibrium segregation or kinetic diffusion processes. Recent work on Nb and Mn doped BaTiO3 highlights the importance of substitutional defects which activate grain boundary trap states and give rise to the PTCR effect. The dynamic interaction of charge carriers with such trap states also produces the rapid electrical breakdown characteristic of varistors. This study explores the issues of defect species, space charge, and electrical transport in donor doped SrTi03 by electron holography and electron energy loss spectroscopy.
The specific defect species and mechanisms of current transport through donor doped SrTiO3 remain unresolved because of the difficulty in connecting defect distributions (structural information) and resultant Schottky barrier effects (chemical information).