Vacancies are the primary mediator for the diffusion of atoms in ions in a large number of solid materials, including crystalline oxides. The study of vacancy mobility and diffusion in bulk materials has myriad technological applications, including in devices that depend on low or high mobility. Both metal and non-metal oxides are of interest. Passivation layers, thermal and electrical insulators, as well high conductivity thermoelectric, electronic, and electrochemical devices depend on stable atomic structures, which can undergo degradation due to vacancy migration when exposed to high temperatures and temperature gradients. A particularly consequential application is the geological confinement of hazardous waste where diffusion can impact the long-term stability of the confinement environment. Vacancy migration can also play a role in other degradation processes, such as corrosion. Diffusion is strongly affected by temperature, vacancy concentration, and other factors, and significant diffusional anisotropy can serve either as a challenge or a benefit in technological design.