ELECTROCHEMICAL INVESTIGATIONS OF SRTIO3 BOUNDARIES

Interfaces (grain boundaries and surfaces) are studied in acceptor (Fe ) doped SrTiO3 bicrystals, single crystals, and ceramics as a function of temperature (423 K less than or equal to T less than or equal to 1 023 K), oxygen partial pressure (1 Pa less than or equal to p(O2) less than or equal to 10(5) Pa), and Fe doping content (1.9.10(18) cm(-3) less than or equal to c(Fe) less than or equal to 9.5.10(19) cm(-3)) u sing electrochemical methods. In particular, Impedance spectroscopy ve been applied. The electrochemical investigation of tilt and twist gra in boundaries in bicrystals combined with structural and chemical grai n boundary charactization by transmission electron microscopy, electro n diffraction x-ray analysis, and electron energy loss spectroscopy al lowed us to clarify grain boundary effects in SrTiO3. The use of rever sible (nonblocking) YBa2Cu3O6+x electrodes proves to be a convenient t echnique to measure conductivities without electrode effects, since bl ocking effects at the sample surface were minimized. These results hav e been compared with those obtained for grain boundaries in polycrysta lline samples as well as with the interfaces between metallic electrod es and SrTiO3 single crystals. Besides individual features, all findin gs at the investigated boundaries and interfaces could be consistently explained by the appearance of pronounced Schottky barriers which wer e composed of depletion layers of mobile majority charge carriers (h(. ), V(o) double over dot).