BZY20 is a mixed ionic-electronic conducting (MIEC) heterovalently doped perovskite that under most conditions is dominantly a proton conductor. In addition to protons, mobile defects include oxygen vacancies and O-site polarons. An important aspect of the present approach is the inclusion of immobile polaron traps that are associated with the yttrium dopant. The BZY20 material can serve as an electrolyte for applications including fuel cells, electrolyzers, and membrane reactors. The principal objective of the present paper is to develop thermodynamic properties (i.e., enthalpies and entropies) for defect-incorporation reactions and transport properties (i.e., diffusion coefficients) for defect transport within the dense ceramic. Previously published conductivity measurements form the basis for fitting the needed property relationships. The paper incorporates the new thermodynamic and transport properties into Nernst-Planck models that characterize defect transport within electrolyte membranes such as in protonic-ceramic fuel cells and electrolyzers. (C) 2018 The Electrochemical Society.