The electrical conductive properties analysis of ytterbium doped calcium zirconate proton conductor solid electrolyte based on crystal defect chemistry

Abstract

Zr-site doped CaZrO₃ is a promising high temperature proton conductor solid electrolyte material used for metal melt hydrogen sensor. To understand the electrochemical properties of ytterbium doped calcium zirconate electrolyte in more detail, the CaZr_1−xYb_xO_3−α (x = 0, 0.025, 0.05, 0.075 and 0.1, hereafter named CZY) solid electrolyte specimens were prepared by use of high temperature solid state reaction process. The structure of the electrolyte samples was characterized by Raman spectrum, XRD and SEM. The densities of the specimens were measured based on Archimedes method. The electrical conductivities of the CZY specimens were measured at the temperature of 573–1373 K in hydrogen-rich or oxygen-rich atmosphere by the two-terminal AC impedance spectroscopy method. The H/D isotope effect of the CZY electrolyte at 973–1373 K was tested to clarify the dominant conducting carrier in predetermined temperature and atmosphere. It is demonstrated that proton is the predominant charge carrier both in oxygen-rich and hydrogen-rich atmosphere at the lower temperature below 1073 K. However, at higher temperature above 1073 K, the dominant charge carrier seems to be to be electron hole in oxygen-rich atmosphere, whereas, oxygen ion vacancy in hydrogen-rich based on the analysis of the atmospheric dependence of the electrical conductivity and the H/D isotope effect. Besides, partial conductivities of conducting species(such as interstitial proton, electron hole and oxygen ion vacancy), the active doping amount of ytterbium and the standard Gibbs free energy changes for interstitial proton production by dissolution of water and hydrogen in the CZY electrolyte were estimated based on crystal defect chemistry theory.