Influence of humidity on the electrical properties of potassium triiodomercurate

The electrical properties of potassium triiodomercurate crystals (KHgI3·H2O) are considerably modified in the presence of water vapour. As a result, this material presents a very high sensitivity to relative humidity (RH). Resistance changes of several orders of magnitude have been observed in triiodomercurate samples (length, cm; section, mm2) within a few tenths of second in the range 25–65% RH under a dc electric field of less than 0.5 V/cm. This behavior has been attributed to the increase of the ionic conductivity in a thin surface layer surrounding the high resistivity core of the samples. This could be induced by fast triiodomercurate dissociation in the presence of water molecules.