Thermodynamic and Electrochemical Transport Properties of Yttrium-Doped Barium Zirconate Stannates

This work explores the structural, microstructural, and high-temperature thermodynamic and electrochemical transport properties of the BaZr 0.8- x Sn x Y 0.2 O 3-δ ( x = 0.2, 0.4, 0.6, 0.8) perovskite system, synthesized via the solid-state reaction method. X-ray diffraction (XRD) and Rietveld refinement confirm the formation of a single-phase cubic perovskite structure for all compositions, with a gradual decrease in lattice parameter as Sn content increases, consistent with the smaller ionic radius of Sn 4+ compared to Zr 4+ . Microstructural analysis shows that increasing Sn content also leads to improved densification. Electrochemical Impedance Spectroscopy (EIS) was employed as a function of both oxygen and water vapor partial pressure (in the temperature range 550–700 °C) to permit the assessment of the thermodynamic and electrochemical transport properties from a defect chemistry model. Van’t Hoff analysis reveals that increasing Zr content leads to more negative hydration enthalpies and higher proton concentrations, due to stronger proton defect stabilization. Proton diffusivity also improves with increasing Zr content, which is supported by lower migration enthalpies. The observed trends are interpreted based on structural tolerance factors, B/A-site electronegativity differences, and lattice parameters, all of which influence proton defect stability and mobility. These insights offer guidance for tailoring Ba-based perovskites for solid-state proton-conducting applications by compositional selection.