ELECTRICAL-PROPERTIES OF SURFACE-LAYERS OF OXIDIC PEROVSKITES

Impedance measurements are performed both on single crystal SrTiO3 and on ceramic BaTiO3 at frequencies between 10 kHz and 10 MHz in the temperature range 300 to 1300 K. The different transport properties of the bulk and the surface region lead to a relaxation like anomaly in the dielectric response. Both the bulk and the surface dielectric properties are inferred by fitting the macroscopic relaxation data. Compared to the bulk properties the oxygen pressure dependent conductivity minimum of the surface region shifts toward higher oxygen pressures. The formation as well as the transport properties of the concerned surface layers are explained by an increased oxygen vacancy concentration within the surface layer which is due to the band bending within the contact region.