Microstructure, Proton Concentration and Proton Conductivity of Barium Zirconate Doped with Ho, Er, Tm and Yb

Acceptor-doped BaZrO 3 is very attractive due to their high proton conductivity in wet atmosphere, enabling a promising application in electrochemical devices. In this work, a systematic investigation on BaZrO 3 doped with Ho, Er, Tm and Yb was performed. The results revealed that, a single perovskite phase was obtained when dopant with the content between 0.02 and 0.3 was introduced, regardless of whether Ho, Er, Tm or Yb was doped. And a bimodal microstructure was observed with the dopant content varying from 0.05 to 0.15. Such bimodal microstructure was found to be composed of large grains with homogeneous composition, and fine grains with discrepancy in composition. Then, through the study on electrochemical conductivity, when the dopant content was between 0.02 and 0.2, the samples doped with Tm was found to have the lowest activation energy for bulk conduction in wet H 2 . Such result indicates that Tm possibly imparts BaZrO 3 with relatively low association energy for proton trapping. Furthermore, a comparison on the total conductivity suggested that BaZr 0.8 Ho 0.2 O 3−δ , BaZr 0.8 Er 0.2 O 3−δ , BaZr 0.8 Yb 0.2 O 3−δ , BaZr 0.8 Tm 0.2 O 3−δ and BaZr 0.75 Tm 0.25 O 3−δ had comparably high value satisfying the criterion (> 0.01 Scm −1 ) for the application as an electrolyte in fuel cells at 600°C.