The defect chemistry methodology is commonly used to interpret the transport properties of materials and to predict the effects of variable working conditions on the electrical properties and processes that depend on mass transport. Analysis of defect diagrams might be far from trivial, even for materials with simple defect structures, and classical methods are thus based on approximate electroneutrality conditions for different regions of the defect diagrams. Those conditions must be carefully selected, and relevant trends of the defect diagrams require time-consuming algebraic re-arrangements of those neutrality conditions with the relevant mass action constants. The transitions between different regions of the defect diagram are poorly described.
The present work proposes an alternative numerical method to solve the overall system without any mathematical simplification. The method has been mainly designed for defect chemistry calculations in oxide materials, using temperature, oxygen partial pressure, and concentrations of additives as independent variables. It is easily extended to include other variables such as the hydrogen and/or water vapor partial pressure. The method also allows simulations of non-equilibrium effects. Mass action constants are combined with the overall neutrality condition and/or mass conservation relations to obtain the concentration of a selected defect versus working conditions. A web application DefChem- Defect Chemistry Toolbox was developed for this purpose. Its applicability is demonstrated for selected case studies. The toolbox is also able to simulate and fit experimental results obtained from different experimental techniques, in particular, from electrical conductivity measurements versus the oxygen partial pressure. The fitting feature can be used to find relevant thermodynamic data for defect chemistry analysis.