Hydration-induced chemical expansion of BaCa(1+y)/3Nb(2−y)/3O3−δ∙xH2O (BCN) and other proton-conducting perovskite oxides

Thermal expansion and chemical strain caused by water uptake were measured for BaCa(1+y)/3Nb(2−y)/3O3−δ∙xH2O (BCN) perovskite-type oxides by dilatometric and X-ray diffraction methods. To describe the total and chemical expansion, we proposed a simple geometric chemical strain model based on the relative change in ionic radii upon hydration. The model calculations agree well with the experimental data for BCN oxides, for which the values of the linear chemical expansion coefficient, β, were found to be around 0.038 per mole of water-filled oxygen vacancies. Next, the model was applied to different perovskite-type proton-conducting oxides with existing literature data on chemical expansion. For example, the values of β, estimated using the model, are around 0.036 and 0.031 for BaZr1−yMyO3−δ and BaCe1−yMyO3−δ, respectively (M = rare-earth metal, Y or Sc). These values are close to those obtained by others using either density functional theory (DFT) calculations or direct experimental measurements, especially given the rather large scatter in the data reported in the literature. The latter is most probably related to the kinetic limitations since, unlike the most oxygen exchange phenomena, humidification of oxides happens at lower temperatures where the slow kinetics of water uptake plays an important role. •Chemical expansion of BaCa(1+y)/3Nb(2-y)/3O3-δ∙xH2O oxides was measured.•Chemical expansion of other state-of-the-art proton-conducting oxides was discussed.•Hydration-induced chemical expansion model for proton-conducting oxides was proposed.•The model proposed allows predicting chemical expansion of a number of oxides.