New Glass Ceramics with High Fluoride Conductivity

摘要

Glass ceramics with fluoride conduction have been prepared by heat treatment of glasses of the system SiO_2-PbO-PbF_2. The influence of the annealing regime on the formation of crystalline phases and on the structure of the glass ceramics has been investigated. The conductivity has been studied at different stages of crystallization. Two different types of crystallization behaviour have been distinguished when glasses are annealed at about 20 K above T_g. Under these conditions only one single crystalline phase arises in the glass matrix. For glasses with up to 15 mol% PbF_2 this crystalline phase is Pb_3Si_2O_7 while at higher PbF_2 content the crystalline phase is PbF_2. Formation of Pb_3Si_2O_7 causes drastical increase of conductivity due to the rise of fluorine concentration in the residual glass. The growth of PbF_2 crystals yields the opposite effect. In some cases, PbF_2 crystals built a continous network throughout the glass matrix. Then, conductivity takes place along grain boundaries and the total conductivity increases again.