Extending Miedema's Semi-Empirical Model to Predict Defect Site Preferences and Formation Enthalpies of Ordered Compounds
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Miedema's Semi-Empirical Model is a method in which a simple calculation provides a rough estimate of the formation enthalpy of a single defect atom (of element X) surrounded completely by a solvent element (element A). The work presented in this paper extends this concept to be applicable in 2 more complex cases. The first case was to use the extended model to determine the site preference of a single defect atom (of element X) that is placed in a highly ordered intermetallic compound (of elements A and B). After analyzing 134 various defect-compound combinations, the overall success of the extended model accurately predicting the defect's site preference was 60.7%. However, with further investigation it was determined that this percentage of success increases in a linear fashion with the absolute difference of the calculated enthalpies of the possible sites of occupancy for the defect. This suggests that the model can be a useful tool for making quick rough estimations as to a defect atoms site preference in highly ordered intermetallic compounds. The second case in which the extended model was applied was for providing an estimation of the formation enthalpy of an intermetallic compound. In this application, the extended model was able to calculation formation enthalpies which were on average between 20% and 30% lower than experimental formation enthalpies.