Many high-temperature electrochemical device components, such as fuel and electrolysis cell electrodes, rely on materials that simultaneously exhibit ionic and electronic conductivity. Rational design of such materials via computational modeling and simulation has long been a challenge due to the complexity of the materials. Materials exhibiting mixed ionic and electronic conductivity (MIECs) tend to be disordered alloys whose composition and stoichiometry are sensitive to the thermodynamic environment. We present here a design framework to predict the ionic and electronic conductivity of candidate disordered perovskite oxide mixtures exhibiting large partial substitutions AA’BB’O3-x on the perovskite sublattices. We demonstrate the approach on the mixed conducting perovskite (Sr)(Ti1-x,Fex)O3-y across the full composition space 0 &lt; x &lt; 1. First-principles electronic structure methods are used to establish defect equilibria and enable prediction of stoichiometry and oxygen vacancy content under different thermodynamic environments. We show that the Sr-Ti-Fe-O composition space can be well-described as a solid solution between the band insulator SrTiO3 and the ordered oxygen vacancy compound Sr2Fe2O5 under a wide variety of temperatures and oxygen partial pressures. Under highly oxidizing or reducing environments, the compositions Sr(Ti1-xFex)O3-x/2+d deviate from the reference composition d = 0, resulting in large p-type or n-type carrier concentrations for d &gt; 0 or d &lt; 0 respectively. These predicted stoichiometries and carrier concentrations are shown to be in good agreement with experiment. To predict ionic diffusivity, a cluster expansion model is built to predict configuration energies and cluster expansion Monte Carlo simulations are used to predict representative alloy configurations under different temperatures and gas environments. The diffusivity tensor is obtained from site and transition state energies as steady-state solutions to the diffusion master equation using a Green’s function approach. This represents a scalable approach to capturing properties such as diffusivity in complex disordered alloy materials. We will also show preliminary results of this application of this framework to the Sr-Ti-Co-O and La-Sr-Co-O perovskite oxide phase space.

Framework for predicting ionic and electronic conductivity in disordered, mixed conducting perovskites

2019 Spring National Meeting

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