Protonic conductivity and photoconductivity studies on H3PW12O40-21H(2)O single crystals

Protonic conductivity measurements are reported for H3PW12O40. 21H(2)O sing le crystals in the temperature range 77 to 303 K. At room temperature, the conductivity is 0.18 Sm-1 and falls to a minimum of 0.26x10(-3) Sm-1 at 188 K. An anomalous behavior in conductivity observed in the temperature range 263 to 283 K is reported and it is essentially due to the disordered struc ture of water molecules. The activation energy determined from the least sq uares analysis in the temperature range 278 to 303 K and 188 to 273 K are 0 .38 and 0.15 eV respectively. The observed conductivity parameter results s upport the vehicle mechanism as the proton conduction mechanism in this sin gle crystal. using the Nernst-Einstein relation, the proton diffusion coeff icient is calculated and found to be 1.29x10(-11) m(2)s(-1) at room tempera ture. Steady state photoconductivity is measured at room temperature for va rious intensities and the material is found to be photosensitive. The varia tion of photocurrent with different illumination levels is found to be line ar in these single crystals. The transient photoconductivity measurement sh ows that the photo-induced responses ape moderate in the beginning and slow during decay process with respect to time.