Use of a Natural Clinoptilolite Monolith as a Negative Temperature Coefficient Thermistor

Geomorphic clinoptilolite, a mechanically and thermally stable mineral substance, has very useful electrical properties due to the presence of extra-framework cations in the crystal structure. Indeed, owing to the electrical transport that alkaline earth metal cations may give, this ceramic material behaves like an electrical insulator at room temperature, while it changes to an electrical conductor with increasing of temperature. Such unusual electrical property of clinoptilolite can be advantageously exploited for a number of functional applications in industrial fields. For example, clinoptilolite-based devices can be used as thermal sensors, electrical/thermal switches, NTC thermistors, etc. Here, the capability of a simple natural clinoptilolite monolith to switch from an electrical insulator to a conductor under fast temperature changes has been investigated via time-resolved a.c. electrical transport measurements.