A qualitative look at the thermodynamics of ternary phase diagrams
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In 2014, Collins’ research group embarked on experiments using Perturbed Angular Correlation (PAC) spectroscopy to measure interactions between solute atoms in ternary alloys. PAC requires a probe atom, 111In, making the systems strictly quaternary, but the probe is present only at the extremely low mole fraction of 10‐11, and has dissolved in almost every phase studied in Collins’s lab in the past. Ideal for measurements of interactions between solute atoms are ternary phases AmBn(X) containing about 1 at.% of X, dissolved on either or both sublattices of the A‐B phase. However, many attempts to make such samples did not yield the desired result. Instead, two alternative outcomes were commonly observed: the solute atom did not dissolve in the host alloy and, instead, retained its elemental crystal structure, or the solute atom reacted with one or other of the two elements, forming an A‐X or B‐X phase, and thereby leaving a depleted A‐B phase. In this thesis, Gibbs free energy diagrams for binary and ternary systems are examined to give insight into the reasons for these outcomes. By looking at the geometry of inferior tangent lines and planes below Gibbs free energy curves and surfaces, one can understand the observed outcomes.