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of GeCl,, SiCl,, and O2 are considered at temperatures and concentrations appropriate to the formation of germanium phosphosilicate glasses for optical communication fiber by the modified vapor deposition process. Using the best available thermodynamic values for the 32 components of the system, good agreement in absolute composition and in the dependence of germanium incorporation with oxygen and the Ge/Si ratio has been shown using an idealsolution approximation for the two condensed-state components. A question remains concerning the best choices of the published critical values of the Gibbs energy of GeOZ(l). Very satisfactory agreement between our experimental results and calculations are obtained using the values published by Pankratz."Using the element potential method to minimize the Gibbs energy of the mixture, a flexible means of calculating the concentrations of very complex chemical equilibria has been demonstrated. Calculated results agree very well with experiment and show that, in so far as the ratio, Ge/Si, is concerned in MCVD glass, the equilibrium is "frozen" at 1650 K and that satisfactorily consistent thermodynamic data have been selected. The model appears robust and its further application to vapor-phase processes for glass formation is warranted. The procedures applied would also be of use in understanding gas-phase equilibria for other electronic materials, for example, 111-V semiconductors.The primary crystalline phase developed in glass-ceramics in the system Pb0-Ba0-Ti02-B203 was investigated. X-ray diffraction and dilatometry were used to identify the primary phase as essentially pure PbTi03. Peak shifts observed in X-ray diffraction patterns resulted from lattice strain due to crystal clamping, and not from (Pb, Ba)Ti03 solid solution formation. Lattice strain was found to increase as the glass-transition temperature of the residual glass increased above the Curie temperature of PbTi03.

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