Solubility and activity of oxygen in liquid germanium and germanium-copper alloys
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6470 ~ + 4.24 (+0.07).
T h e s t a n d a r d f r e e e n e r g y o f s o l u t i o n o f o x y g e n in l i q u i d g e r m a n i u m is c a l c u l a t e d f r o m t h e s a t u r a t i o n s o l u b i l i t y , a n d r e c e n t l y m e a s u r e d v a l u e s f o r t h e f r e e e n e r g y of f o r m a t i o n o f G e O 2 , a s s u m i n g t h a t o x y g e n o b e y s S i e v e r t ' s l a w up t o t h e s a t u r a t i o n l i m i t . F o r t h e reaction,
I/2 O2(g) -- OGe AG° =-39,000 + 3.21 T (+500) cal =-163,200 + 13.43 T (+2100) J. where the standard state for dissolved oxygenis that whichmakes the value of activity equal to the concentration (in at. pct), in the limit, as concentration approaches zero. The effect of copper on the activity of oxygen dissolved in liquid germanium is found to be in good agreement with that predicted by a quasichemical modelin which each oxygenwas assumed to be bonded to four metal atoms and the nearest neighbor metal atoms to an oxygen atom are assumed to lose approximately half of their metallic bonds.
PREVIOUS
studies' on dilute solutions of oxygen were mainly confined to typical metallic systems in which there are fewer electrons than needed to form electron-pair bonds to all nearest neighbors. Investigation of the behavior of dissolved oxygen in group IVA elements like germanium, whichis a covalently bonded and tetrahedrally coordinated semiconductor in the solid state, and of its alloy with group I B elements such as copper, in whichthe electron concentration changes rapidly with composition, is a natural extension of earlier studies. RecentlyJacob and AIcockS have completed a similar study using an isopiestic technique on oxygensolubility in liquid galliumcopper alloys in which there is a well understood change in electron-atom ratio, and whilst the results indicate the predicted effects they do not cover the whole composition range. Furthermore information on liquid Ge-O and Cu-Ge-O systems is useful from a practical as well as a theoretical point of view. A knowledge of the oxygensolubility in liquid germanium is important in the preparation of germanium based semiconductors grownfrom melts. Recent models1,3 for the description of thermodynamic properties of oxygenin dilute solution in binary K. FITZNER was on leave at the Department of Metallurgy and Materials Science, University of Toronto, when this investigation was undertaken. He has now returned t o the Institute for Metals Research, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow, Poland, K. T . JACOB is Senior Research Associate and Special Lecturer, Department of Metallurgy and Materials Science, University of Toronto, and C. B. ALCOCK is Professor, Department of Metallurgy and Materials Science, University of T o r o n t o , T o r o n t o , Canada M 5 S 1A4. Manuscript submitted August 3 1 , 1976. METALLURGICAL
TRANSACTIONSB
alloys differ with respect to the significance of metalmetal interaction in the ternary solution. The equations developedby Jacob and AlcockI for predicting the activi
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