S. PAGOLA; R. E. CARBONIO; J. A. ALONSO; M. T. FERNÁNDEZ-DÍAZ

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 1997 vol. 134 p. 76 - 76

p style="TEXT-ALIGN: justify; MARGIN: 0cm 0cm 10pt" class="MsoNormal">The crystal structure of the columbite-type phase MgNb2O6 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) Å. The structure contains chains of NbO6 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 MgO6 octahedra sharing corners. This compound contains Nb5+ with electronic configuration d0. 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–