K2NaOsO5.5 and K3NaOs2O9: The first osmium perovskites containing alkali cations at the “A” site

K2NaOsO5.5 and K3NaOs2O9 were obtained from solid-state reactions of potassium superoxide, sodium peroxide and osmium metal at elevated oxygen pressures. K2NaOsO5.5 crystallizes as an oxygen-deficient cubic double perovskite in space group Fm  3¯m with a=8.4184(5) Å and contains isolated OsO6 octahedra. K3NaOs2O9 crystallizes hexagonally in P63/mmc with a=5.9998(4) Å and c=14.3053(14) Å. K3NaOs2O9 consists of face sharing Os2O9 pairs of octahedra. According to magnetic measurements K2NaOsO5.5 is diamagnetic, whereas K3NaOs2O9 displays strong antiferromagnetic coupling (TN=140 K), indicating enhanced magnetic interactions within the octahedral pair.

High oxidation states of Os, obtained by high oxygen pressure synthesis, are accommodated in double and triple perovskite matrices. K3NaOs2O9 displays enhanced magnetic interactions.Figure optionsDownload as PowerPoint slideHighlights
► New osmates containing highly oxidized Os were obtained by high O2 pressure synthesis.
► High oxidation states of Os are accommodated in double and triple perovskite matrices.
► Both compounds represent the first Os perovskites with an alkali metal at the A site.
► K3NaOs2O9 displays enhanced magnetic interactions within the octahedral pair.