Crystal Structure Refinement of MgNb2O6Columbite from Neutron Powder Diffraction Data and Study of the Ternary System MgO–Nb2O5–NbO, with Evidence of Formation of New Reduced Pseudobrookite Mg5−xNb4+xO15−δ(1.14≤x≤1.60) Phases
✍ Scribed by S. Pagola; R.E. Carbonio; J.A. Alonso; M.T. Fernández-Dı́az
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 465 KB
- Volume
- 134
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The crystal structure of the columbite-type phase MgNb 2 O 6 has been refined from powder neutron diffraction data. The compound is orthorhombic, space group Pbcn (60), Z ؍ 4, with unit cell parameters a ؍ 14.1875(1), b ؍ 5.7001(1), c ؍ 5.0331(1) A > . The structure contains chains of NbO 6 octahedra sharing edges along the c axis, which are arranged in double layers through common corners. The double layers, parallel to the bc plane, are connected via MgO 6 octahedra sharing corners. This compound contains Nb 5؉ with electronic configuration d 0 . Attempts to obtain new materials with Nb in a mixed valence state were made in the ternary system MgO-Nb 2 O 5 -NbO. For molar ratios Mg : Nb ؍ 1 : 2 new pseudobrookite-type phases have been identified. They have the general composition Mg 5؊x Nb 4؉x O 15-, with x values ranging from 1.14 to 1.60. The compounds Mg 4 Nb 2 O 9؊ (corundum-type) and Mg 3 Nb 6 O 11 were identified when the Mg : Nb ratio was 4 : 2. All the reduced materials were also characterized by thermogravimetric analysis.