EVOLUTION WITH TIME OF PROPERTIES OF THE POLYTETRABROMO-P-PHENYLENEDISELENIDE DOPED WITH AN HALOGEN (CL OR I)

PBrPDSe has been doped by chlorine or iodine. The samples have been studied by X ray photoelectron spectroscopy (XPS), electron spin resonance (E.S.R.) and with a scanning electron microscope equiped with an electronic microprobe. Conductivity measurements have also been performed on pressed pellet samples. In the case of chlorine doped polymer, it is shown by XPS study that chlorine decomposes progressively the polymer. This result is corrobored by ESR study. The conductivity of the I2 doped PBrPDSe exhibits an increase by about three orders of magnitude. The doping concentration decreases with time from 30 at % to 5 at % but the ESR signal stays the same. The high value of g anisotropy and the XPS peak of Se show that the positive charge is localized on the Se atoms. The binding energy of the iodine anion corresponds to I5- species after doping and to I3- thirteen months later. All these results can be explained by the reaction I5- --> I2 + I3-. The I2 removing explains the decrease of the iodine concentration and the I3- formation explains the stability of the ESR signal. The microphotographs show that the surface of the fibrils of iodine doped powder become rough with time this may be explained by I2 removing and surface modification. These modifications can explain the decrease with time of the conductivity.