Correlation between Phase Behavior and Electrical Conductivity of 10 mol % Y-Doped BaZrO: An Anomalous Dispersion Effect-Aided Synchrotron Radiation XRD Study Combined with TEM Observation and Electrochemical Analysis.

Y-doped BaZrO (BZY) has high proton conductivity and is a promising electrolyte candidate for fuel cells and electrolytic cells at an intermediate temperature range. However, the conductivity of BZY has a large discrepancy in the literature. In particular, for BaZrYO (BZY10), the reported bulk conductivity varies in the range of more than 2 orders of magnitude. With the aim of revealing the reason, in this work, we conducted synchrotron radiation X-ray diffraction analysis on a BZY10. The X-ray was adjusted to 17.027 keV to approach the Y-K absorption edge (17.037 keV), and the anomalous dispersion effect was thereby activated for a precise distinction between Zr and Y. High-resolution scanning transmission electron microscopy observation and electrochemical measurements were also performed. Assisted by these experimental results, Rietveld refinement with greatly improved quality was thereby available to generate precise information on both the phase behavior and crystal structure. The results revealed that the BZY10 samples after sintering at 1600 °C for 8 to 200 h have a bimodal microstructure. They were not single phases, but mixtures of two perovskite phases differing slightly in Y contents. The Y contents in the two phases after sintering for 8 h were about 12.3 and 8.7 mol %, respectively, and finally became 10.6 and 9.2 mol %, respectively, after sintering for 200 h. In addition, the partition of Y over both the Ba and Zr sites was not suggested, although small Ba-deficiency around 0.05 formed in the sample sintered for 40 h or longer. But notably, the formation of the Ba vacancies is reasonably believed as the possible reason for the decrease in bulk and also grain boundary conductivities.