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Thermionic work functions and desorption energies for oxygen on polycrystalline W, Mo and Re filaments, discussing oxygen pressure and filament temperature
Cs8Ta6O19 crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. Cs1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cs–O bond distances ranging from 2.93–3.42 Å. There are four inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.83–2.39 Å. In the second Ta5+ site, Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.83–2.39 Å. In the third Ta5+ site, Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.83–2.39 Å. In the fourth Ta5+ site, Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.84–2.36 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to four equivalent Cs1+ and one Ta5+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Cs1+ and two Ta5+ atoms. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Cs1+ and two Ta5+ atoms. In the fourth O2- site, O2- is bonded in an octahedral geometry to six Ta5+ atoms. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to four equivalent Cs1+ and one Ta5+ atom.
Cs3TaO8 crystallizes in the tetragonal I-42m space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded to eight O atoms to form CsO8 hexagonal bipyramids that share corners with four equivalent TaO8 hexagonal bipyramids, corners with four equivalent OCs3TaO trigonal bipyramids, and edges with two equivalent TaO8 hexagonal bipyramids. There are four shorter (3.07 Å) and four longer (3.26 Å) Cs–O bond lengths. In the second Cs site, Cs is bonded in a 4-coordinate geometry to twelve O atoms. There are a spread of Cs–O bond distances ranging from 3.03–3.56 Å. Ta is bonded to eight O atoms to form distorted TaO8 hexagonal bipyramids that share corners with four equivalent CsO8 hexagonal bipyramids, corners with four equivalent OCs3TaO trigonal bipyramids, and edges with two equivalent CsO8 hexagonal bipyramids. There are four shorter (2.03 Å) and four longer (2.08 Å) Ta–O bond lengths. There are two inequivalent O sites. In the first O site, O is bonded to three Cs, one Ta, and one O atom to form distorted OCs3TaO trigonal bipyramids that share a cornercorner with one CsO8 hexagonal bipyramid, a cornercorner with one TaO8 hexagonal bipyramid, corners with ten equivalent OCs3TaO trigonal bipyramids, and an edgeedge with one OCs3TaO trigonal bipyramid. The O–O bond length is 1.51 Å. In the second O site, O is bonded in a 1-coordinate geometry to five Cs, one Ta, and one O atom.
Cs3Ta5O14 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are three inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cs–O bond distances ranging from 3.27–3.42 Å. In the second Cs1+ site, Cs1+ is bonded in a 1-coordinate geometry to nine O2- atoms. There are a spread of Cs–O bond distances ranging from 2.86–3.55 Å. In the third Cs1+ site, Cs1+ is bonded in a 1-coordinate geometry to seven O2- atoms. There are a spread of Cs–O bond distances ranging from 2.79–3.44 Å. There are four inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with five TaO6 octahedra and a cornercorner with one TaO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 28–43°. There are a spread of Ta–O bond distances ranging from 1.90–2.20 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra, corners with three equivalent TaO5 trigonal bipyramids, and an edgeedge with one TaO6 octahedra. The corner-sharing octahedral tilt angles are 35°. There are a spread of Ta–O bond distances ranging from 1.94–2.27 Å. In the third Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 35–43°. There are a spread of Ta–O bond distances ranging from 1.96–2.07 Å. In the fourth Ta5+ site, Ta5+ is bonded to five O2- atoms to form TaO5 trigonal bipyramids that share corners with five TaO6 octahedra and an edgeedge with one TaO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 40–57°. There are a spread of Ta–O bond distances ranging from 1.85–2.16 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Cs1+ and two Ta5+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ta5+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cs1+ and two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Cs1+ and two equivalent Ta5+ atoms. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cs1+ and two Ta5+ atoms. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to one Cs1+ and two equivalent Ta5+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two Cs1+ and two Ta5+ atoms. In the eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Cs1+ and two Ta5+ atoms. In the ninth O2- site, O2- is bonded in a distorted water-like geometry to two equivalent Cs1+ and two equivalent Ta5+ atoms. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to two Cs1+ and two Ta5+ atoms.
CsTaO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Cs1+ is bonded to twelve equivalent O2- atoms to form CsO12 cuboctahedra that share corners with twelve equivalent CsO12 cuboctahedra, faces with six equivalent CsO12 cuboctahedra, and faces with eight equivalent TaO6 octahedra. All Cs–O bond lengths are 2.93 Å. Ta5+ is bonded to six equivalent O2- atoms to form TaO6 octahedra that share corners with six equivalent TaO6 octahedra and faces with eight equivalent CsO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–O bond lengths are 2.07 Å. O2- is bonded in a distorted linear geometry to four equivalent Cs1+ and two equivalent Ta5+ atoms.