Effects of rare earth Sc2O3 doping on the phase composition, diffusion rate and conductivity of CaHf1−xScxO3−δproton conductor

Abstract

To explain the electrochemical performance of Sc2O3 doped orthogonal CaHfO3, in the temperature range of 973 to 1473 K, the conductivity of this series of electrolyte samples in oxygen rich atmosphere and hydrogen rich atmosphere was measured by using the two terminal AC method. The conductivity first increases and then decreases with the increases of Sc2O3 doping amount; it reaches a maximum at the Sc3+ concentration of x = 0.18. Furthermore, doping with Sc3+ improves the conductivity of the electrolyte CaHf1−xScxO3−δ and reduces its conductivity activation energy. By examining the H / D isotope effect and the electromotive force of electrolyte samples, it is found that CaHf1−xScxO3−δ is a pure proton conductor between 973 and 1273 K. Furthermore, the chemical diffusion coefficients of the CaHf1−xScxO3−δ are about 1.25 × 10−6 to 1.61 × 10−5 cm2 s−1 in the temperatures range of 973 to 1473 K, that is to say, the response speed of the CaHf1−xScxO3−δ is very sensitive. Study found that proton is the major carrier in this electrolyte in both a hydrogen rich atmosphere and an oxygen rich atmosphere. Moreover, at higher temperatures of 1373 to 1473 K, positive holes are the primary carriers in an oxygen rich atmosphere.