Perovskite-Structured BaScO₂(OH) as a Novel Proton Conductor: Heavily Hydrated Phase Obtained via Low-Temperature Synthesis

Abstract

A novel proton-conducting material, BaScO2(OH) has been successfully fabricated. The known high-temperature proton conductors are typically perovskite-type oxides, in which the proton concentration is determined by hydration reaction of oxygen vacancies introduced by a small amount of acceptor dopant. On the other hand, the novel material BaScO2(OH) is still associated with the A2+B4+O3 perovskite structure but with the B-site cation fully consisting of an acceptor cation Sc3+, which facilitates to retain an appreciable amount of protonic defects. While it is difficult to obtain the material by simply hydrating the unhydrated form (Ba2Sc2O5), a combination of a new low-temperature sol–gel synthesis and ultrahigh-pressure (4 GPa) compaction at room-temperature enables us to obtain the heavily hydrated phase BaScO2(OH) due to on-synthesis hydration. The BaScO2(OH) synthesized has been proved to be a pseudocubic perovskite phase with XRD and Raman analyses. The thermal dehydration analyses have verified the composition BaScO2(OH) in terms of proton concentration, and their mobile nature has been observed with in situ FT-IR analysis. The protonic conductivity of the material is as high as 1.7 × 10–2 S·cm–1 at 500 °C, which is well higher than the total conductivity of the best proton-conducting perovskite oxides at intermediate temperature range.