Synthetic β‐Spodumene and several β‐Spodumene‐silica solid solutions were prepared, and their thermal expansion behavior was studied using high‐temperature X‐ray diffraction techniques. Data indicate that all β‐Spodumenes are characterized by a pronounced anisotropy of thermal expansion much the same as that of the silica polymorph keatite. Anisotropy increases slightly and the volume expansion decreases as the compositions become richer in SiO2. Specimens with more than 80.8 wt% SiO2 at 130O°C and 1 atm contain P‐cristobalite along with β‐Spodumene. The lattice parameters of β‐Spodumene compositions throughout the solid solution range were determined. The structural aspects of the anisotropy of thermal expansion are discussed.

Thermal Expansions and Chemical Modificationsof Cordierite IV . Conclusion 629 0 A 0 \ O \ 50 60 70 80 f rnol % Ag I Fig. 3. Composition dependence of glass transition temperature., T,, of glasses in the pseudobinary system AgI-Ag,GeO,. Values of T , in the systems AgI-Ag,MoO, (Ref. 1) and AgI-Ag,PO, (Ref. 3) are shown for comparison.Ag,P04.3 These systems are all simple salt (AgI) and silver orthooxysalts. The glasses in the systems AgI-Ag,MoO, and AgI-Ag3P04 are composed of discrete ions Ag', I-, and Ma4'-or P 0 , 3 -, 6 3 7 as expected from the chemical composition, leading to low T,'s. In comparison, the Tg's of the glasses in the present system are high. Since the glasses consist of the structural units Ge06 and GeO,, the chemical composition indicates that the glasses must contain condensed macroanions of these units. The higher values of T , are consistent with the preceding structural evidence.Conductivities for 17 glass compositions in the glass-forming region were to &l.cm-l at room temperature. The composition dependence of conductivity of the glasses differs from that of other superionic conducting glasses composed of tetrahedral structural units and is explained by the difference in the short-range atomic arrangement,I4 which is consistent with the present conclusions. X-ray diffraction analysis is now in progress to determine the coordination number of oxygen to germanium in the present glasses.

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