The electronic structure of pristine and doped (100) tilt grain boundaries in SrTiO3

To understand the electronic properties of doped grain boundaries, we reviewed the atomic scale techniques currently available to study the electronic structure at pristine SrTiO(3) grain boundaries. The knowledge gained from the pristine boundaries is used to interpret experimental and theoretical results from a Mn doped Sigma 5 SrTiO(3) grain boundaries. Mn atoms are shown to preferentially substitute at specific Ti sites at the grain boundary core. Furthermore, the formal oxidation state of the Mn atoms at the grain boundary core was found to be reduced compared to the Mn atoms substituting for Ti in the bulk. This change of valence did not, however, significantly affect the atomic structure of the grain boundary, as determined by Z-contrast imaging and electron energy-loss spectroscopy, which revealed similar fine-structure features at both the doped and pristine grain boundary. We conclude, therefore, that composition and atomic structure have different effects on the local electronic structure and should be treated separately in any segregation and electrical conductivity models for grain boundaries.