ADSORPTION-INDUCED UNUSUAL CHANGES IN THE ELECTRICAL-CONDUCTIVITY OF SOME FERROCENE DERIVATIVES

The effects of adsorption of different organic vapors on the electrical conductivity of some ferrocene derivatives have been studied using the sandwich cell technique. A conductivity peak is observed in the plot of measured current versus temperature for a sandwich cell of powdery material with some adsorbed vapors. The dependence of the intensity of the peak and the temperature at which it appears have been studied as a function of grain size of powdery materials, heating rate, amount of adsorbed vapor, and also the nature of the adsorbed vapors. At the vapor-adsorbed state these materials show very high value of activation energy and the pre exponential factor sigma-o (in the usual semiconduction equation). Results indicate that the adsorption is a physical adsorption. The usual mechanisms for the adsorption-induced change in conductivity and activation energy are not suitable for explaining the observed results. Adsorption induced reversible structural phase transition seems responsible for the anomalous behavior of the adsorption-induced changes in the electrical properties of these materials. The results obtained with different ferrocene derivatives have been compared with that of ferrocene and possible reason for the adsorption induced phase transition is discussed.