Ab initio determination of the novel perovskite-related structure of La{sub 7}Mo{sub 7}O{sub 30} from powder diffraction
- Univ. du Maine, Le Mans (France). Lab. des Fluorures
- Inst. Laue Langevin, Grenoble (France)
A new mixed valence molybdate, La{sub 7}Mo{sub 7}O{sub 30}, first prepared by high energy ball milling, has been successfully synthesized by controlled hydrogen reduction of La{sub 2}Mo{sub 2}O{sub 9}. Its original crystal structure was determined from X-ray and neutron powder diffraction (space group R{sub 3}; a = b = 17.0051(2) {angstrom}, c = 6.8607(1) {angstrom}; Z = 3; reliability factors: R{sub p} = 0.081, R{sub wp} = 0.091, {chi}{sup 2} = 3.1, R{sub Bragg} = 0.049, R{sub F} = 0.033). It consists in the hexagonal stacking of individual cylinders of perovskite-type arrangement. These cylinders are built up from perovskite cages sharing corners in trans-position along their diagonal axis. Two different mixed-valence molybdenum sites coexist, with more (Mo{sup +5.75}) or less (Mo{sup +4.5}) distorted octahedral environments. Lanthanum atoms are located within the perovskite cages and around them, very close to their regular positions in the perovskite structure. Lanthanum and molybdenum atoms thus form two rows of almost perfect cubes, shifted from each other by c/2. An electron microscopy study revealed the defect-free cationic and octahedral arrangements in the (a,b) plane.
- OSTI ID:
- 329135
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 142; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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