Toughening of Y-doped BaZrO3 proton conducting electrolytes by hydration

In BaZr1-xYxO3-x/2 (BZY), the state-of-the-art oxide proton conductors, the proton conductivity is facilitated by hydration of oxygen vacancies. Hydration induces lattice expansion, which may induce stress and thereby potentially reduce the mechanical integrity of fuel cells. Here, we report on the effect of hydration/dehydration on the mechanical properties of dense BZY-materials sintered by two different methods. The chemical expansion due to hydration was determined by X-ray diffraction, and the normalized chemical strain was calculated by combining these data with thermogravimetry. The mechanical properties were investigated by the Vickers-micro indentation technique. Hydration was demonstrated to enhance the fracture toughness of the materials with the change in fracture mode from intergranular to transgranular mechanisms. We demonstrate that the hydration/dehydration process is reversible and discuss the present findings with respect to the long-term stability of electrochemical devices based on BaZrO3.