Calculation of defect chemistry using the CALPHAD approach

The defect chemistry of the perovskite phase LaMnO3 +/- d is modeled using the compound energy formalism and an associate model. In both cases the CALPHAD methodology is applied meaning that all thermodynamic and phase diagram data of the phase is simultaneously and consistently reproduced. The differences between the two modeling methods are discussed and the descriptions are submitted to a defect chemistry analysis. It is shown that the compound energy formalism is able to perfectly describe the defect chemistry of the perovskite phase whereas the associate model fails to correctly reproduce it. When using the associate model the choice of which associates to use plays a crucial role on how well the system can be approximated. As the associates are not physically meaningful entities this choice must be made arbitrarily. In the case of the compound energy formalism on the other hand a more physically realistic description of the system is achieved and fewer optimizing parameters are required. The reason for this is that the model description of the phase within the compound energy formalism is unambiguously constructed based on measured physical properties of the phase. The advantage of the associate model is that the model description is simple compared to the rather cumbersome expression obtained for the compound energy formalism. (c) 2005 Elsevier Ltd. All rights reserved.