Sol-gel synthesis using alkoxides is employed to obtain fluorine-modified BaZr0.8Y0.2O3-δ nanopowders with Ba excess at 750 °C. Possible effects of F loss at high temperature were limited on densifying at the low temperature of 1200 °C for 4 h on addition of ZnO as sintering agent. The presence of F in sintered samples was confirmed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry. XPS and Raman spectroscopy indicated that F doping of BZY inhibits carbonate formation. Conductivity measurements for prolonged periods in wet H2-containing and CO2-containing atmospheres at 500 °C also demonstrated chemical stability. The temperature dependence of the electrical conductivity of sintered samples in wet and dry N2 and O2 indicates that the grain-boundary dominates the electrical behaviour to 500 °C, above which the bulk process dominates. Ionic conduction is prevalent at low temperature, with a transition to a mixed ionic-electronic conducting behaviour at 450 °C.

We thank MICINN in Spain for the concession of projects RTI2018–095088-B-I00, RTI2018–095373-J-I00 and predoctoral grant BES-2016–077023. The technical and other support provided by Daniel Gamarra (Facility of Analysis and Characterization of Solids and Surfaces of SAIUEx, financed by UEX, Junta de Extremadura, MICINN, FEDER and FSE) is recognised.

Appendix A. Supplementary material

Peer reviewed