Heteroanionic materials, which contain two or more anionic species, offer compositional and structural flexibility not found in otherwise analogous homoanionic materials . As such, controlling the relative stoichiometries and crystallographic arrangements of the anion species in heteroanionic materials allows their properties to be tuned . This compositional and structural versatility means that heteroanionic materials find applications across a range of critical technologies, including thermoelectrics , photocatalysis , and energy storage .