Synthesis and crystal structure determination of Tl{sub 8}Nb{sub 27.2}O{sub 72} using TEM and single-crystal X-ray diffraction
- Univ. de Picardie Jules Verne, Amiens (France). Lab. de Reactivite et de Chimie des Solides
- Univ. de Caen (France)
- Ecole Nationale Superieure de Chimie de Lille, Villeneuve d`Ascq (France)
An investigation of the Nb-Tl-O system has allowed the synthesis of a new phase, Tl{sub 8}Nb{sub 27.2}O{sub 72}. This phase is structurally and chemically close to a Tl-Nb-O phase previously described as a builtup hexagonal bronze with a {approx} 7.4 {angstrom}, b {approx} 13 {angstrom}, c {approx} 7.6 {angstrom}, and an orthorhombic C-type lattice. The electron diffraction study evidences a doubling of the c parameter with regard to the C cell, resulting in an orthorhombic I-type lattice with, in addition, the observation of a second superstructure and twinned microdomains. A structural determination of the mean orthorhombic I-type cell was successfully carried out by combining energy dispersion spectroscopy (EDS) and single-crystal XRD studies and leads to a = 7.534(7) {angstrom}, b = 12.992(12) {angstrom}, c = 15.555(12) {angstrom}, Z = 8, space group Im2m, R = 0.097, and R{sub w} = 0.099 from 995 independent reflections. A chemical formula for this thallium niobate, Tl{sub 8}Nb{sub 27.2}O{sub 72}, consistent with EDS results, was deduced by structure refinement. HREM investigations on this phase clearly show irregular occupancy of the supplementary crystallographic positions by niobium atoms together with a monocommensurate modulated structure and twinned microdomains.
- OSTI ID:
- 642184
- Journal Information:
- Journal of Solid State Chemistry, Vol. 135, Issue 2; Other Information: PBD: 1 Feb 1998
- Country of Publication:
- United States
- Language:
- English
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