Si–Cr alloy is one of the predominant solvents for rapid solution growth of 4H–SiC crystals. The solubilities of carbon in Si–40 mol%Cr alloy at SiC saturation at 1773–2273 K and in Si–Cr alloys of various chromium contents at 2073 K were measured by equilibrating the Si–Cr alloy with a 4H–SiC single crystal. Carbon solubility in Si–40 mol%Cr alloy increased with temperature from 0.22 mol% at 1773 K to 3.59 mol% at 2273 K. At 2073 K, carbon solubility at SiC saturation increased with the chromium content in the liquid from 0.18 mol% in Si–20 mol%Cr to 16.4 mol% in Si–80 mol%Cr. A thermodynamic analysis of the Si–Cr–C alloy was also conducted. Although the sub-regular solution model is often adopted to estimate phase relations in solution systems, this predicted a carbon solubility in Si-40 mol%Cr at SiC saturation more than two times higher than the measured value. In contrast, a quasi-chemical model that considered the competition between substitutional Si and Cr atoms bonding to interstitial carbon atoms reproduced the activity coefficient of carbon in Si–Cr alloys of 60–100 mol%Si composition, in which the carbon solubility at SiC saturation was less than 1.5 mol%, fairly well. This quasi-chemical model enabled the precise phase relation to be evaluated when designing the solution growth of SiC using a Si–Cr solvent.
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