Glass ceramics which exhibited fluoride-ion conductivity were prepared by heat treating compositions in this system. The conductivity was studied at various stages of crystallization, and 2 different types of crystallization behavior were identified when the glasses were annealed at about 20K above the glass transition temperature. Under these conditions, only a single crystalline phase appeared in the glass matrix. In glasses with up to 15mol%PbF2, this crystalline phase was Pb3Si2O7. At higher PbF2 contents, the crystalline phase was PbF2. The formation of Pb3Si2O7 caused a sharp increase in conductivity, due to an increased F concentration in the residual glass. The growth of PbF2 crystals had the opposite effect. In some cases, the PbF2 crystals formed a continuous network throughout the glass matrix. Conductivity then occurred along grain boundaries, and the total conductivity again increased.

S.Goldammer, H.Kahnt: Berichte der Bunsengesellschaft für Physikalische Chemie, 1996, 100[9], 1531-4