Experimental study and thermodynamic analysis of phase equilibria in the silicon-rich part of the Si-Sr and Si-Ba systems

Using thermal and activation analysis techniques, we have constructed the liquidus curves in the primary crystallization fields of silicon in the Si-Sr and Si-Ba systems. The Sr and Ba solid solubilities in silicon have been determined using microhardness measurements, and have been shown to exhibit retrograde behavior. At 1573 K, the solubility of Sr in silicon is 1.15 at %, and that of Ba is 0.98 at %. The solidus and liquidus curves have been analyzed using thermodynamic modeling and the known thermodynamic properties of the melt and intermediate phases. We assume that the large deviations of the melts from ideal behavior are due to the formation of Zintl polyanions (or clathrates), and describe a model for the chemical structure of the silicon-rich melts.