DOE OSTI2020
Ca3UO6 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six equivalent UO6 octahedra. The corner-sharing octahedra tilt angles range from 36–44°. There are a spread of Ca–O bond distances ranging from 2.31–2.39 Å. In the second Ca2+ site, Ca2+ is bonded in a 4-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.33–2.94 Å. In the third Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.35–2.84 Å. U6+ is bonded to six O2- atoms to form UO6 octahedra that share corners with six equivalent CaO6 octahedra. The corner-sharing octahedra tilt angles range from 36–44°. There are a spread of U–O bond distances ranging from 2.07–2.12 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded to three Ca2+ and one U6+ atom to form distorted corner-sharing OCa3U trigonal pyramids. In the second O2- site, O2- is bonded in a 3-coordinate geometry to four Ca2+ and one U6+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one U6+ atom. In the fourth O2- site, O2- is bonded to three Ca2+ and one U6+ atom to form distorted corner-sharing OCa3U tetrahedra. In the fifth O2- site, O2- is bonded in a 5-coordinate geometry to four Ca2+ and one U6+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one U6+ atom.