Hydrated doped-BaZrO3 proton conductors studied by positron annihilation lifetime spectroscopy

Abstract

The study of defect chemistry for doped BaZrO3 proton conductors is of particular interest because of defect interactions that can affect the proton conductivity of the material. Protons incorporated due to the material's hydration can be trapped by negatively charged immobile dopants, reducing proton mobility. The reduction of the proton conduction impedes the use of BaZrO3 materials in energy conversion applications at intermediate temperatures (300 °C – 600 °C). The probing of proton trapping in doped BaZrO3 is hindered by the limited availability of techniques sensitive to defect chemistries. In this work, we used positron annihilation lifetime spectroscopy (PALS) to study the defect chemistry of Y-doped and Sc-doped BaZrO3. Using a two-state positron trapping model we showed that PALS can be applied to study the defect chemistry of hydrated dense proton conductors. Positron trapping rates and lifetimes were correlated with doping levels of the materials. Probability significance t-tests were carried out for PALS parameters to verify whether there are differences/similarities for various populations: non-doped/doped, level and type of doping, high temperature, and surface effects. The results revealed that the initial doping generates a significant number of traps available for positrons. Doping with yttrium increased the positron trapping rate, while this effect was not observed with scandium. Low-temperature hydration affects specimens significantly inhibiting positron trapping at undoped BaZrO3 material and highly doped specimens. Positronium formation in rough surface layers, and highly doped specimens was detected but does not exceed 1%.