Preparation and structure of K8Ca2U6O24, K8Sr2U6O24, and K8Ba2U6O24

K8Ca2U6O24, K8Sr2U6O24, and K8Ba2U6O24 were synthesized by solid-state reactions of their respective oxides at 850°C. The structure of the compounds was derived from powder X-ray diffraction data, and structural parameters were refined by the Rietveld profile method. All the compounds are isostructural and belong to the cubic space group Im3m. The structure consists of uranyl octahedra and regular octahedra of oxygen atoms around Ca, Sr, or Ba atoms. Each potassium ion is surrounded by two types of oxygen atoms in 12-coordination geometry.