The defects in the perovskite materials of A1303-types show a tendency to accumulate in the form of linear or extended defects such as dislocation, shear planes and stacking faults. On the basis of SIMS measurements utilising tracer techniques and the observation of etch pits it is shown for model perovskite such as SrTi03 that the density of dislocations near the surface is of the order 109/cm2 and that these defects form an interconnected network. These defects provide easy diffusion paths which take the role of "short circuits".