Effect of heating rate on positive-temperature-coefficient-of-resistivity behavior of conductive composite thin films

A phenomenon was discovered that leads to the selective detection of abrupt increases in the temperature of conductive composite thin films consisting of conductive ceramic fillers and an insulating polymer matrix. Examining the heating rate dependence of the positive-temperature-coefficient-of-resistivity (PTCR) effect provided information about this intelligent phenomenon. The anomalous PTCR effect was observed above 0.3 degrees C min(-1) for all the prepared films. However, the magnitude of the anomaly decreased when the heating rate decreased below 0.1 degrees C min(-1), and when the heating rate further decreased below 0.04 degrees C min(-1), the anomalous resistivity-temperature relationship disappeared. The results suggest that these thin films can selectively detect abrupt increases in temperature, which could lead to an intelligent mechanism. Our results also suggest a PTCR mechanism, in which the expansion of crosslinked polymers in the thermodynamic nonequilibrium state essentially produces the anomaly. (C) 1998 American Institute of Physics. [S0003-6951(98)03251-3].