Experimental determination of intrinsic parameters in double-donor-doped (Ba0.92Sr0.08)TiO3-based positive temperature coefficient ceramics

In the present work, double-donor-doped (Ba0.92Sr0.08)TiO3-based positive temperature coefficient (PTC) ceramics were fabricated for potential application in an over-current protector. The electrical properties of the materials were also characterized. Using the experimental results obtained, theoretical models on electrical properties were studied, and the intrinsic parameters were determined. The relationship between the intrinsic parameters, the materials variables and the electrical properties was discussed. It was noted that the addition of double donors Y2O3+Nb2O5 could result in relatively low room-temperature resistivity, in particular, 30 Ω cm at the sintering temperature of 1230 deg. C. Within the investigated working temperature range, the grain-boundary potential barrier at a fixed measuring temperature decreased with increasing sample sintering temperature. The evaluated effective donor concentration and surface acceptor state density were in good agreement with the reported values in the literature. A parameter was introduced based on these two variables to represent the resistivity jump. The depletion layer thickness was determined to be in the submicron range. The present work is believed to be the first report to determine, based on the experimental data, all the essential intrinsic parameters for double-donor-doped PTC ceramics