Dynamics of non-equilibrium nanostructure in a proton-conducting ceramic

Proton-conducting ceramics have attracted interest as moderate-temperature proton conductors for applications such as energy conversion and hydrogen production. Effects of topological defects and interfacial hydrated layers on proton transport and concerns about structural degradation make understanding nanostructure dynamics crucial for improving structural stability and proton transport. However, material polycrystallinity, absorption, and reactive operating conditions have prevented detailed in-situ measurements of the nanostructure dynamics. Here, we find experimentally in-situ in yttrium-doped barium zirconate, an archetypal proton conductor, that contrary to the assumptions of structural stability the nanostructure is unexpectedly dynamic at temperatures as low as 200 °C. We achieve this by applying coherent X-ray diffraction to a BaZr0.8Y0.2O3-d sintered pellet to image in-situ three-dimensional nanostructure inside the constituent grains in a humid nitrogen atmosphere. We directly observe non-equilibrium defect generation and subsequent grain cracking on a timescale of hours, forming new, otherwise energetically unfavorable facets in BaZr0.8Y0.2O3-d. Furthermore, structural rearrangements correlate with dynamic inhomogeneities of the lattice constant within the grains, showing potential heterogeneous H+ transport. We provide an approach to in-depth in-situ studies of nanostructure dynamics in proton-conducting ceramics and demonstrate unexpectedly active evolution of grain boundary and non-equilibrium defect networks, with implications for functional properties from structural stability to proton transport.