Clean and hydrated low-index Rb₂Ti₂O₅ surfaces

Despite the remarkable dielectric properties of Rb₂Ti₂O₅ upon exposure to a humid atmosphere, its surfaces are still poorly known, to date. Here we study the atomic-scale structure of the clean (100), (010) and (001) surfaces, and the onset of water adsorption via density functional theory. Among them, the clean (001) surface has a very low surface energy, much smaller than most terminations of other perovskites or titania. Rb₂Ti₂O₅ (001) is also very reactive towards water, which adsorbs as a molecule, forming regular water arrays on the surface. From the calculations, we conclude that Rb₂Ti₂O₅ could very easily cleave under ambient conditions, forming (001) planes with ordered adsorbed water and almost null surface stress. Although Rb₂Ti₂O₅ is a three-dimensional crystal, it behaves in this respect as a two-dimensional compound, such as graphite or layered perovskites.