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Crystal Structure of BaNb 6.3(1) Ti 3.6(1) O 16 containing Nb 6 O 12 , fused Ti 3 O 13 Clusters and Ti 3 O 10 Units
Author(s) -
Nilsson Göran,
Svensson Gunnar
Publication year - 2000
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/(sici)1521-3749(200001)626:1<160::aid-zaac160>3.0.co;2-w
Subject(s) - crystallography , octahedron , supercell , monoclinic crystal system , superstructure , crystal structure , substructure , crystallite , materials science , crystal (programming language) , tetrahedron , diffraction , group (periodic table) , triclinic crystal system , chemistry , physics , programming language , computer science , thunderstorm , structural engineering , optics , organic chemistry , meteorology , engineering , thermodynamics
A new phase, BaNb 6.3(1) Ti 3.6(1) O 16 , has been synthesised. Electron diffraction studies indicate an hexagonal substructure with unit cell parameters a ≈ 8.9 Å and c ≈ 9.5 Å. In some of the ED patterns superstructure reflections are present, indicating a supercell with a = √3 · a sub and c = c sub . However, X‐ray single‐crystal diffraction studies of a crystallite yielding reflections corresponding to the supercell revealed it to be monoclinic, with the unit cell parameters a = 26.811(2) Å, b = 15.4798(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°. The average crystal structure was refined, using the subcell with a = 8.937(2) Å, b = 15.479(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°, space group Cm11, and Z = 4, to R I = 3.24% and R wI = 3.44%. The structure can be described as an hexagonal close packing layers of Nb 6 octahedra, Ba, and O atoms (A1, A2) and layers of O atoms (B1, B2), appearing in the packing sequence: A1B1A2B2. The Nb 6 octahedra are found in isolated Nb 6 O 12 O 6 clusters, and the Ti atoms in Ti 3 O 13 and Ti 3 O 10 units in octahedral and tetrahedral voids formed by O atoms, respectively. The Ti positions were found to be only partly occupied. Microanalysis indicates that some Nb atoms are located in the Ti 3 triangles. A model is presented that interprets these not fully occupied Ti 3 triangles as a result of a superimposing of three different structures. Two of these consist of two fused Ti 3 O 13 units, forming an Ti 6 O 19 unit, and a Ti 3 O 10 unit, while the third consists of alternating Ti 3 O 13 units.