Materials Data on K4Hf5O12 by Materials Project
K4Hf5O12 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are three shorter (2.69 Å) and six longer (2.97 Å) K–O bond lengths. In the second K1+ site, K1+ is bonded to twelve O2- atoms to form KO12 cuboctahedra that share corners with six equivalent KO12 cuboctahedra, faces with three equivalent KO12 cuboctahedra, and faces with seven HfO6 octahedra. There are a spread of K–O bond distances ranging from 2.91–3.27 Å. There are three inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. There are three shorter (2.05 Å) and three longer (2.20 Å) Hf–O bond lengths. In the second Hf4+ site, Hf4+ is bonded to six equivalent O2- atoms to form HfO6 octahedra that share corners with six equivalent HfO6 octahedra and faces with six equivalent KO12 cuboctahedra. The corner-sharing octahedral tilt angles are 7°. All Hf–O bond lengths are 2.09 Å. In the third Hf4+ site, Hf4+ is bonded to six O2- atoms to form distorted HfO6 octahedra that share corners with three equivalent HfO6 octahedra and faces with four equivalent KO12 cuboctahedra. The corner-sharing octahedral tilt angles are 7°. There are three shorter (1.97 Å) and three longer (2.31 Å) Hf–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to four K1+ and two Hf4+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three K1+ and three Hf4+ atoms.