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
1997; Elsevier BV; Volume: 134; Issue: 1 Linguagem: Inglês
10.1006/jssc.1997.7538
ISSN1095-726X
AutoresSilvina Pagola, Raúl E. Carbonio, J. A. Alonso, M. T. Fernández‐Díaz,
Tópico(s)Microwave Dielectric Ceramics Synthesis
ResumoThe crystal structure of the columbite-type phase MgNb2O6has been refined from powder neutron diffraction data. The compound is orthorhombic, space groupPbcn(60),Z=4, with unit cell parametersa=14.1875(1),b=5.7001(1),c=5.0331(1) Å. The structure contains chains of NbO6octahedra sharing edges along thecaxis, which are arranged in double layers through common corners. The double layers, parallel to thebcplane, are connected via MgO6octahedra sharing corners. This compound contains Nb5+with electronic configurationd0. Attempts to obtain new materials with Nb in a mixed valence state were made in the ternary system MgO–Nb2O5–NbO. For molar ratios Mg:Nb=1:2 new pseudobrookite-type phases have been identified. They have the general composition Mg5−xNb4+xO15−δ, withxvalues ranging from 1.14 to 1.60. The compounds Mg4Nb2O9−δ(corundum-type) and Mg3Nb6O11were identified when the Mg:Nb ratio was 4:2. All the reduced materials were also characterized by thermogravimetric analysis.
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