PTC Sensor Materials

Abstract

Publisher Summary This chapter provides description about positive temperature coefficient (PTC) sensor materials. For a semiconductor to possess a large PTC, it must exhibit some anomaly in its electrical conductivity mechanism. The resistivity–temperature characteristics of semimetallic semiconductors over a wide temperature range show the presence of three distinct regions: two regions at low and high temperature and a third (middle) region with a PTC. In doped pure barium titanate, the temperature at which the PTC region commences during heating is rigidly fixed by a change in the crystallographic structure from tetragonal to cubic and corresponds to the ferroelectric Curie temperature of the material. The early applications of PTC thermistors made use of the low-voltage switching characteristic of the resistance–temperature relationship as an over-temperature protection device. A PTC thermistor can also be used to control current between two predetermined limits over a wide range of applied voltage and temperature. The applications of plastic PTC materials include energy limiting for power supplies; the overload protection of wiring, resistors, loudspeakers, and pulse and duty-cycle circuits; and short-circuit protection for batteries.