V//2 O//3 COMPOSITE THERMISTORS.

The semiconductor to metal phase transition found in vanadium (III) oxide, V//2 O//3 , was incorporated into a composite thermistor which exhibits a negative temperature coefficient (NTC) as well as a positive temperature coefficient (PTC) resistance effect. The composites were prepared using V//2 O//3 and several polymers including a flexible epoxy, a polyurethane and crystalline polyethylene. These composites showed large PTC resistivity effects of up to eight orders of magnitude. Depending on the type of polymer chosen, the transition temperature at which the PTC phenomenon occurs can be changed. In addition, an NTC effect was observed at the temperature of the semiconductor to metal transition of the metal oxide filler. The resistivity vs. temperature curve resembles a square well with three different conducting ranges: semiconductor to metal to insulator. Finally, the percolation curves for polyethylene composites were found to be a function of filler particle size.