The Ionic Conduction Properties in Scandium Doped Calcium Zirconate High Temperature Proton Conducting Solid Electrolyte

Abstract

To gain a more thorough understanding of the conductive mechanism of Sc-doped CaZrO₃ electrolyte, solid electrolyte specimens of CaZr_{1 − x}Sc_xO_{3 − δ} (with x values of 0.06, 0.12, 0.18, and 0.24, hereinafter referred to as CZS) were meticulously prepared using a high-temperature solid-state method. The phase structure of the electrolyte was thoroughly analyzed using X-ray diffraction (XRD). The electrical conductivity of the CZS electrolyte was rigorously tested within a temperature range of 573 to 1473 K, both in oxygen-rich and hydrogen-rich atmospheres, employing the two-terminal AC impedance spectroscopy method. Additionally, the H/D isotope effect of the electrolyte at various temperatures in both H₂ and D₂ atmospheres was meticulously examined through AC impedance spectroscopy. The electromotive force (EMF) of the electrolyte was precisely measured by a high-impedance ohmmeter at temperatures ranging from 573 to 1273 K. Furthermore, based on crystal defect chemistry theory, estimates were made for the partial conductivities of the conducting species, the active doping concentration of Sc, and the standard Gibbs free energy changes associated with the production of interstitial protons through the dissolution of water and hydrogen within the CZS electrolyte. The results clearly indicated that protons serve as the primary charge carrier in both oxygen-rich and hydrogen-rich atmospheres at temperatures below 1073 K. However, as temperatures rise above 1073 K, the situation changes: in hydrogen-rich atmospheres, oxygen ion vacancies emerge as the dominant charge carrier, whereas in oxygen-rich atmospheres, electron holes take precedence. Notably, CZY stands out as a promising candidate for a proton-conducting electrolyte material, suitable for high-temperature hydrogen sensors.