A new family of anti-perovskite oxyhydrides with tetrahedral GaO 4 polyanions.

New solid compounds A 3- x GaO 4 H 1- y (A = Sr, Ba; x ∼0.15, y ∼0.3), which are the first oxyhydrides containing gallium ions, have been synthesized by high-pressure synthesis. Powder X-ray and neutron diffraction experiments revealed that the series adopts an anti-perovskite structure consisting of hydride-anion-centered HA 6 octahedra with tetrahedral GaO 4 polyanions, wherein the A- and H-sites show partial defect. Formation energy calculations from the raw materials support that stoichiometric Ba 3 GaO 4 H is thermodynamically stable with a wide band gap. Annealing the A = Ba powder under flowing Ar and O 2 gas suggests topochemical H - desorption and O 2- /H - exchange reactions, respectively.