Gel Synthesis and Crystallization of Sodium Tetragermanate Glass Powders

Sodium tetragermanate gel (Na2O.4GeO2) was synthesised by hydrolytic polycondensation of germanium ethoxide with sodium ethoxide in alcoholic medium. Crystallisation behaviour of the gel, examined by differential thermal analysis and x-ray diffraction, is reported and discussed. Sodium tetragermanate gel crystallises in two steps. In the primary transformation, at about 575-degrees-C, metastable Na2Ge4O9 crystals are formed as the major crystalline phase with a small amount of Na4Ge9O20 crystals. In the second transformation at higher temperatures metastable Na2Ge4O9 are converted to the thermodynamically stable Na4Ge9O20. These results are compared with those of the conventionally prepared glass