SFB-Kolloquium Welch

Hydroxyperovskites: an overlooked group of potential functional materials

While there is enormous interest in studying oxide perovskites with stoichiometries based upon or derived from ABO₃, including oxygen-deficient compositions and organometallics, other closely related topologies have been overlooked. Hydroxyperovskites are such a group. Their structures are perovskite-like octahedral frameworks with vacant cavity A sites, and all oxygen atoms form hydroxyl groups. There are fifteen naturally occurring hydroxyperovskites and numerous synthetic analogues. There are two stoichiometries: BB′(OH)₆ and B(OH)₃. The former consist of alternating divalent and tetravalent cations (B = Mg, Ca, Mn²⁺, Fe²⁺, Co²⁺, Cu²⁺, Zn; B′ = Sn, Ge). B(OH)₃ structures have only trivalent cations (Al, Sc, Fe³⁺, Ga, In). The recent discovery of a natural proton deficient hydroxyperovskite Fe³⁺GeO₆H₅, the mineral nancyrossite, suggests the possibility of novel H behaviour in these materials that may arise from the creation of transient vacant H sites in a structure with dynamic proton disorder. This talk will summarize our current knowledge of the crystal chemistry of hydroxyperovskites and will highlight productive areas of research for exploring their potential as low-temperature protonic conductors.