Capacitance of single crystal and low-angle tilt bicrystals of Fe-doped SrTiO3.

We used a.c. impedance spectroscopy to study the capacitance of single crystal and bicrystal Fe-doped SrTiO3. Measurements performed on a single crystal sample indicate unequivocally that the bulk dielectric permittivity is dependent on defect concentration. Three symmetrical [001] tilt bicrystals with misorientation angles theta = 2.3, 5.4 and 7.8 degrees were examined. The area specific capacitances obtained for the 5.4 and 7.8 degrees boundaries are consistent with values predicted from a one-dimensional double-Schottky-barrier model. For the 2.3 degrees boundary, more complex behaviour was observed. This is attributed to the electrical non-uniformity of the interface becoming significant at large dislocation separation. The effects of a d.c. bias on the impedance of the bicrystals was also investigated.