VISUALIZATION OF THE GRAIN-BOUNDARY POTENTIAL BARRIERS OF PTC-TYPE BATIO3 CERAMICS BY CATHODOLUMINESCENCE IN AN ELECTRON-PROBE MICROANALYZER

In PTC-type BaTiO3 ceramics the grain-boundary potential barriers can easily be made visible by means of cathodoluminescence in an electron-probe microanalyzer without having a voltage applied. The visualization can be explained in the context of our finding that the intensity of the cathodoluminescence radiation depends sensitively on the number of charge carriers present in the conduction band. Thus, in PTC-type BaTiO3 ceramics, but not in undoped or reduced materials, the deficiency of conduction electrons in the depletion layers at the grain boundaries causes a blackening of the grain-boundary regions. The blackening of the grain boundaries of our PTC ceramics also appears below the Curie point, thus demonstrating the existence of grain-boundary barriers in this temperature range.