Solute Trapping: Comparison of Theory with Experiment

The dependence of the nonequilibrium partition coefficient $k$ of Bi in Si upon solidification velocity $v$ has been measured with sufficient accuracy to distinguish between proposed solute-trapping mechanisms. For the range of measured velocities, 2-14 m/s, we observe a much more gradual increase in $k$ with increasing $v$ than those previously reported and no evidence for a "saturation" effect, i.e., $\frac{\mathrm{dk}}{\mathrm{dv}}\to 0$ at $k<\mathrm{}1\mathrm{}$. The continuous-growth model of Aziz fits the data quite well; the Aziz stepwise-growth model and the two-level Baker model yield values of $\frac{\mathrm{dk}}{\mathrm{dv}}$ that are too high.