Pyroelecticity: Triglycine sulfate crystal growth and characterization

(advanced laboratory project)

Yu.Preezant & Y.Preezant

Spring, 2003

Abstract

Ferroelectric crystals are an interesting class of materials. They are similar phenomenologically to ferromagnetic materials in that they exhibit hysteresis loops, spontaneous polarization, and coercive field. Ferroelectric crystals have a number of practical applications, and one of those is a pyroelectric infrared (PIR) detection.

PIR devices can detect a person moving into or through a detection zone with high reliability. The slightest positive or negative thermal radiation change in contrast to a background, focused by the appropriate optics, triggers the sensor element. There is no interference between neighboring units due to the passive nature of the detection principle.

At the heart of every PIR detector is the pyroelectric crystal. Typical detectors use materials, such as triglycine sulfate (TGS) or lithium tantalite. They are ferroelectric crystals, which have a maximum pyroelectric sensitivity at room temperature and therefore do not require the cooling for detection of temperature changes. And both TGS and lithium tantalite exhibit a large spontaneous electrical polarization below their Curie points.

Triglycine sulfate is a water-soluble crystal and it is a joint in the armour of this crystal from the point of view its stability in the environment. But indeed for this reason we chose to grow a triglycine sulfate crystal. A water solubility of TGS allows growing it from the water solution by evaporation. So we planed to obtain a TGS crystal and make a PIR detector from it.

Report  => download now (1.04Mb)

Pictures

Crystallizer

scheme and more photos...

 
TGS Crystals grown in our experiments

more photos...

Measurements setup

scheme and more photos...