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-resi stivity (PTCR) effect provided information about this intelligent phenomeno n. The anomalous PTCR effect was observed above 0.3 degrees C min(-1) for a ll 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 heati ng rate further decreased below 0.04 degrees C min(-1), the anomalous resis tivity-temperature relationship disappeared. The results suggest that these thin films can selectively detect abrupt increases in temperature, which c ould lead to an intelligent mechanism. Our results also suggest a PTCR mech anism, in which the expansion of crosslinked polymers in the thermodynamic nonequilibrium state essentially produces the anomaly. (C) 1998 American In stitute of Physics. [S0003-6951(98)03251-3].