Electrical and Structural Characterization of a Low-Angle Tilt Grain Boundary in Iron-Doped Strontium Titanate

The atomistic structure and electrical properties of a symmetrical 5.4° 001] tilt grain boundary in Fe-doped SrTiO₃ have been investigated, respectively, by means of various transmission electron microscopy (TEM) techniques and impedance spectroscopy. In weak-beam dark-field images, the grain boundary is revealed to consist of a periodic array of dislocations; high-resolution TEM images show that the dislocation cores are separated by regions of strained lattice. The impedance response of the bicrystal has been measured in the frequency range 20 Hz ≤ f ≤ 10⁶ Hz as a function of temperature and oxygen partial pressure. The transport of charge across the array of dislocations that form the grain boundary is strongly hindered. Analysis of the impedance data in terms of a double-Schottky-barrier model yields a space-charge potential that exhibits a weak dependence on temperature and oxygen partial pressure and is ～0.55 V in the investigated regime.