Electrical conductivities of low-alkali and alkali-free glasses and glass ceramics

Glasses and glass-ceramics that do not contain alkali oxides have low bulk electrical conductivities under normal conditions which increase somewhat with temperature; such materials are used as high-temperature insulators in electrical and radio engineering. If the temperature is only slightly above the room value, low-alkali glass-ceramics can be used. The conductivities of glasses and glass-ceramics were examined in the systems: Li2O-Al2O3-SiO2-TiO2, Li2O-Al2O3-SiO2-P2O5(Ag2O), MgO-Al2O3-SiO2-TiO2-CeO2, MgO(MnO)-Al2O3-SiO2-TiO2, ZnO-Al2O3-SiO2-TiO2, and BaO(CaO,SrO)-Al2O3-SiO2-TiO2. Conductivities were measured by the two-electrode method in the range 300-800 K. The mineral compositions of the crystalline phases, the temperature dependence of conductivity, and the activation energy of the glasses and glass-ceramics are indicated. Good electrical characteristics occur in ceramics derived from glasses containing 4% Li2O. The conductivities at 470-540 K are in the range 10 exp(-6) to 10 exp(-8) S/m, and increase smoothly on heating. Glasses not containing alkali oxides have similar values at 690-790 K, and ceramics at 590-690 K. The glass-ceramics in these systems were recommended as insulating materials operating over wide temperature ranges.