Studies in Lithium Oxide Systems: XIII, Li,O.Al2O3.2SiO2‐Li2O.Al2O3.2GeO2

Complete solid solubility was demonstrated to occur between LiAlGeO4 and the low temperature form of Li AlSiO2 (a-eucryptite). Hydrother-mal preparation was necessary for the silicate-rich compositions. Under atmospheric pressure, about 65 mole % LiAlGeO4 entered the β-eucryβ-tite phase at 1150°C, but solid solutions containing more than 25 mole % LiAlGeO4 exsolved if held at lower temperatures. Directional thermal expansion data were obtained by X-ray diffraction methods on both α- and β-eucryptite and their solid solutions. Substitution of Ge4+ for Si4+ produced no significant difference in the thermal expansion coefficients in the α and β phases. An increase in the lattice parameters in the a and c directions took place as expected when Ge4+ (0.53 A) was substituted for Si4+ (0.39 A).