RARE EARTH PHOSPHATES AS HUMIDITY SENSORS

Abstract

The aim of this work is preparation, characterization, and evaluation of some rare earth phosphates REPO4 (RE= La, Sm, Gd) to be used as humidity sensors. Their substitution with Na+ or Ca2+ were prepared by both wet and dry methods. The produced samples were characterized by using the classical methods. The X-ray data shows that different compounds and different phases were formed depending on the method of preparation and the control conditions. The electrical conductivity of the samples were measured at 25-300°C and different relative humidity ranges of 30 to 92%. The dependence of electrical conductivity on temperature indicates that, the rare earth phosphates behave as semiconductor materials whatever they prepared by wet or dry method. It is found that the electrical conductivity of most phosphate samples increase smoothly as the relative humidity increase. This behavior may due to the protonic conduction at low humidity values and to the protonic and electrolytic conductions at high humidities. From the analysis of the obtained results, it may conclude that, the humidity sensors with high sensitivity and thermal stability could be developed from some rare earth phosphates.