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Title: Chemical twinning of the pyrochlore structure in the system Bi{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}

Abstract

New ternary bismuth iron niobates having structures based on chemical twinning of pyrochlore are described. Bi{sub 5.67}Nb{sub 10}FeO{sub 35} has hexagonal symmetry, P6{sub 3}/mmc, a=7.432(1)A, c=31.881(2)A, Z=2 and Bi{sub 9.3}Nb{sub 16.9}Fe{sub 1.1}O{sub 57.8} has rhombohedral symmetry, R-3m, a=7.433(1)A, c=77.488(2)A, Z=3. The structures of both phases were determined and refined to R{sub 1}=0.04 using single-crystal X-ray data. They can be described as being derived from the pyrochlore structure by chemical twinning on (111){sub py} oxygen planes. The chemical twin operation produces pairs of corner-connected hexagonal tungsten bronze (HTB) layers as in the HTB structure, so the structures may alternatively be described as pyrochlore:HTB unit-cell intergrowth structures. In the hexagonal phase the pyrochlore blocks have a width of 12A, whereas the rhombohedral phase has pyrochlore blocks of two widths, 6 and 12A, alternating with HTB blocks. It is proposed that the previously reported binary 4Bi{sub 2}O{sub 3}:9Nb{sub 2}O{sub 5} phase has a related structure containing pyrochlore blocks all of width 6A. A feature of the structures is partial occupancy ({approx}65%) of the Bi sites and displacement of the Bi atoms from the ideal pyrochlore A sites towards the surrounding oxygen atoms, as observed in Bi-containing pyrochlores.

Authors:
 [1];  [2];  [3];  [3];  [4]
  1. CSIRO Minerals, Box 312, Clayton South, Vic., 3169 (Australia), E-mail: ian.grey@csiro.au
  2. CSIRO Minerals, Box 312, Clayton South, Vic., 3169 (Australia)
  3. National Institute of Standards and Technology, Materials Science, and Engineering Laboratory, Gaithersburg, MD 20899 (United States)
  4. Equipe CEA-CNRS NPSC SP2M/DRFMC/CEA, 17 rue des Martyrs, 38054 Grenoble (France)
Publication Date:
OSTI Identifier:
21015632
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 1; Other Information: DOI: 10.1016/j.jssc.2006.10.004; PII: S0022-4596(06)00539-1; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BISMUTH OXIDES; FERRITES; HCP LATTICES; IRON OXIDES; LAYERS; MONOCRYSTALS; NIOBATES; NIOBIUM OXIDES; PYROCHLORE; SYMMETRY; TUNGSTEN BRONZE; TWINNING

Citation Formats

Grey, I.E., Mumme, W.G., Vanderah, T.A., Roth, R.S., and Bougerol, C. Chemical twinning of the pyrochlore structure in the system Bi{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.10.004.
Grey, I.E., Mumme, W.G., Vanderah, T.A., Roth, R.S., & Bougerol, C. Chemical twinning of the pyrochlore structure in the system Bi{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}. United States. doi:10.1016/j.jssc.2006.10.004.
Grey, I.E., Mumme, W.G., Vanderah, T.A., Roth, R.S., and Bougerol, C. Mon . "Chemical twinning of the pyrochlore structure in the system Bi{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}". United States. doi:10.1016/j.jssc.2006.10.004.
@article{osti_21015632,
title = {Chemical twinning of the pyrochlore structure in the system Bi{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}},
author = {Grey, I.E. and Mumme, W.G. and Vanderah, T.A. and Roth, R.S. and Bougerol, C.},
abstractNote = {New ternary bismuth iron niobates having structures based on chemical twinning of pyrochlore are described. Bi{sub 5.67}Nb{sub 10}FeO{sub 35} has hexagonal symmetry, P6{sub 3}/mmc, a=7.432(1)A, c=31.881(2)A, Z=2 and Bi{sub 9.3}Nb{sub 16.9}Fe{sub 1.1}O{sub 57.8} has rhombohedral symmetry, R-3m, a=7.433(1)A, c=77.488(2)A, Z=3. The structures of both phases were determined and refined to R{sub 1}=0.04 using single-crystal X-ray data. They can be described as being derived from the pyrochlore structure by chemical twinning on (111){sub py} oxygen planes. The chemical twin operation produces pairs of corner-connected hexagonal tungsten bronze (HTB) layers as in the HTB structure, so the structures may alternatively be described as pyrochlore:HTB unit-cell intergrowth structures. In the hexagonal phase the pyrochlore blocks have a width of 12A, whereas the rhombohedral phase has pyrochlore blocks of two widths, 6 and 12A, alternating with HTB blocks. It is proposed that the previously reported binary 4Bi{sub 2}O{sub 3}:9Nb{sub 2}O{sub 5} phase has a related structure containing pyrochlore blocks all of width 6A. A feature of the structures is partial occupancy ({approx}65%) of the Bi sites and displacement of the Bi atoms from the ideal pyrochlore A sites towards the surrounding oxygen atoms, as observed in Bi-containing pyrochlores.},
doi = {10.1016/j.jssc.2006.10.004},
journal = {Journal of Solid State Chemistry},
number = 1,
volume = 180,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}