DOE OSTI2020
Ba2Ni3O8 crystallizes in the orthorhombic Pmm2 space group. The structure is two-dimensional and consists of one Ba2Ni3O8 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with eight BaO12 cuboctahedra, faces with five BaO12 cuboctahedra, faces with four equivalent NiO6 octahedra, and faces with four equivalent NiO5 square pyramids. There are a spread of Ba–O bond distances ranging from 2.76–2.87 Å. In the second Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with eight BaO12 cuboctahedra, faces with five BaO12 cuboctahedra, faces with four equivalent NiO6 octahedra, and faces with four equivalent NiO5 square pyramids. There are a spread of Ba–O bond distances ranging from 2.76–2.87 Å. There are three inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded to five O2- atoms to form NiO5 square pyramids that share a cornercorner with one NiO6 octahedra, corners with four equivalent NiO5 square pyramids, and faces with four equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Ni–O bond distances ranging from 1.95–2.21 Å. In the second Ni4+ site, Ni4+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four equivalent NiO6 octahedra, corners with two NiO5 square pyramids, and faces with eight BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Ni–O bond distances ranging from 1.91–1.96 Å. In the third Ni4+ site, Ni4+ is bonded to five O2- atoms to form NiO5 square pyramids that share a cornercorner with one NiO6 octahedra, corners with four equivalent NiO5 square pyramids, and faces with four equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Ni–O bond distances ranging from 1.95–2.20 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ba2+ and two equivalent Ni4+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ba2+ and two equivalent Ni4+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to four Ba2+ and two equivalent Ni4+ atoms. In the fourth O2- site, O2- is bonded to four equivalent Ba2+ and two Ni4+ atoms to form a mixture of distorted edge and corner-sharing OBa4Ni2 octahedra. The corner-sharing octahedra tilt angles range from 0–6°. In the fifth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ba2+ and two equivalent Ni4+ atoms. In the sixth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ba2+ and two equivalent Ni4+ atoms. In the seventh O2- site, O2- is bonded to four equivalent Ba2+ and two Ni4+ atoms to form a mixture of distorted edge and corner-sharing OBa4Ni2 octahedra. The corner-sharing octahedra tilt angles range from 0–6°. In the eighth O2- site, O2- is bonded in a distorted linear geometry to four Ba2+ and two equivalent Ni4+ atoms.