Beware of the water: Hidden hydrogenation of perovskite membranes made by the water-soluble sacrificial layer method

The fabrication of perovskite oxide free-standing films (membranes) by lift-off methods using water-soluble sacrificial layers such as Sr₃Al₂O₆ is appealing because of the new possibilities that these membranes present over conventional epitaxial films. However, little is known about how the fabrication process itself, and in particular the exposure to water during the etching step, affects their properties. Here, we investigate how membranes of two perovskite archetypes, antiferroelectric PbZrO₃ and paraelectric SrTiO₃, are affected by this fabrication process. We find evidence that hydrogen penetrates the perovskite structure. Concomitant with this protonation, the functional properties also change, and both materials display ferroelectric-like behavior that is absent in bulk or in hydrogen-free films at room temperature. We also find that thermal annealing can be used to expel the hydrogen from the membranes, which henceforth recover their bulklike properties.