PROTONIC CONDUCTIVITY OF LAYERED ZIRCONIUM PHOSPHONATES CONTAINING -SO3H GROUPS .3. PREPARATION AND CHARACTERIZATION OF GAMMA-ZIRCONIUM SULFOARYL PHOSPHONATES

Five gamma-layered zirconium phosphonates containing sulfophenyl, sulf obenzyl, as well as mono- and di-fluorinated sulfobenzyl groups in the interlayer region, have been prepared by topotactic exchange starting from gamma-zirconium phosphate in the hydrogen form. They were charac terised for their composition, interlayer distance and thermal stabili ty. Conductivity measurements were carried out at 100 degrees C as a f unction of relative humidity. At 5% relative humidity, the ac conducti vity extends over the range 10(-5)-10(-6) S cm(-1) the sulfophenyl and the difluoro-sulfobenzyl phosphonates being the most conductive compo unds. However, the conductivities of all five compounds become progres sively closer and tend to the same upper limit as the relative humidit y approaches 100%. The highest conductivity (0.05 S cm(-1)) was measur ed for gamma-zirconium sulfophenyl phosphonate at 100 degrees C and 95 % relative humidity. Combined ac/dc measurements, carried out on the l atter compound at 100 degrees C and 47% relative humidity, have proved the conduction process to be of the protonic type. Considerations bas ed on conductivity and surface area data indicate that the conduction process is mainly due to bulk proton transport.