STUDY ON ELECTRICAL AND RADIOCRYSTALLOGRA PHIC PROPERTIES OF THE SOLID FLUORITE SOLUTION IN THE SYSTEM PBF TEF4-TEO2

A new non-stoichiometric lead-tellurium oxide fluoride with a disorder ed anion-excess fluorite-type structure has been synthesized in the so lid state and characterized. Its compositional range at 200 degrees C has been defined within the PbF2-TeO2-TeF4 system. Its ionic conductiv ity has been measured and its change with composition analyzed for the three solid solutions Pb1-xTexF2+2nPb1-xTexF2Ox (0 less than or equal to x less than or equal to 0.20) and Pb1-xTexF2-2xO2x (0 less than or equal to x less than or equal to 0.70). In each case, a conductivity minimum associated with a maximum activation energy has been observed for very low extents of tellurium doping x. For the Pb1-xTexF2+2x phas e, a significant increase in the conductivity sigma and of the fluorit e subcell parameter a(F) was observed for x approximate to 0.1. This c orresponds to the occurrence of a complex modulated superstructure. Th e partially ordered PD0.80Te0.20F2.40 phase is a good anionic conducto r with an electrical performance of the same order as that of the best fluorides known to date.