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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}
}
  • The refinement of the Bi{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}–Sb{sub 2}O{sub 5} system phase diagram has been performed and the existence of the two ternary compounds has been confirmed. The first one with a pyrochlore-type structure (sp. gr. Fd 3-barm) exists in the wide solid solution region, (Bi{sub 2−x}Fe{sub x})Fe{sub 1+y}Sb{sub 1−y}O{sub 7±δ}, where x=0.1–0.4 and y=−0.13–0.11. The second one, Bi{sub 3}FeSb{sub 2}O{sub 11}, corresponds to the cubic KSbO{sub 3}-type structure (sp. gr. Pn 3-bar) with unit cell parameter a=9.51521(2) Å. The Rietveld structure refinement showed that this compound is characterized by disordered structure. The Bi{sub 3}FeSb{sub 2}O{sub 11} factor groupmore » analysis has been carried out and a Raman spectrum has been investigated. According to magnetization measurements performed at the temperature range 2–300 K it may be concluded that the Bi{sub 3}FeSb{sub 2}O{sub 11} magnetic properties can be substantially described as a superposition of strong short-range antiferromagnetic exchange interactions realizing inside the [(FeSb{sub 2})O{sub 9}] 3D-framework via different pathways. - Graphical abstract: The refinement of the Bi{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}–Sb{sub 2}O{sub 5} system phase diagram has been performed and the existence of the solid solution with a pyrochlore-type structure (sp. gr. Fd 3-barm) and Bi{sub 3}FeSb{sub 2}O{sub 11}, correspond of the cubic KSbO{sub 3}-type structure (sp. gr. Pn 3-bar has been confirmed. The structure refinement, Raman spectroscopy as well as magnetic measurements data of Bi{sub 3}FeSb{sub 2}O{sub 11} are presented. - Highlights: • The Bi{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}–Sb{sub 2}O{sub 5} system phase diagram refinement has been performed. • The Bi{sub 3}FeSb{sub 2}O{sub 11} existence along with pyrochlore structure compound is shown. • It was determined that the Bi{sub 3}FeSb{sub 2}O{sub 11} is of disordered cubic KSbO{sub 3}-type structure. • Factor group analysis of Bi{sub 3}FeSb{sub 2}O{sub 11} vibrational spectrum has been performed. • Short-range antiferromagnetic interactions govern Bi{sub 3}FeSb{sub 2}O{sub 11} magnetic behavior.« less
  • Subsolidus phase relations have been determined for the Bi{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Nb{sub 2}O{sub 5} system in air (900-1075 deg. C). Three new ternary phases were observed-Bi{sub 3}Fe{sub 0.5}Nb{sub 1.5}O{sub 9} with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi{sub 17}Fe{sub 2}Nb{sub 31}O{sub 106} and Bi{sub 17}Fe{sub 3}Nb{sub 30}O{sub 105} that appear to be structurally related to Bi{sub 8}Nb{sub 18}O{sub 57}. The fourth ternary phase found in this system is pyrochlore (A{sub 2}B{sub 2}O{sub 6}O'), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi{sub 2}FeNbO{sub 7}) suggesting that {approx}4-15% of the A-sites are occupiedmore » by Fe{sup 3+}. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co iad of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi{sub 2}O{sub 3}:Fe{sub 2}O{sub 3}:Nb{sub 2}O{sub 5} using neutron powder diffraction data is reported with the A cations displaced (0.43A) to 96g sites and O' displaced (0.29A) to 32e sites (Bi{sub 1.721}Fe{sub 0.190}(Fe{sub 0.866}Nb{sub 1.134})O{sub 7}, Fd3-bar m (no. 227), a=10.508(1)A). This displacive model is somewhat different from that reported for Bi{sub 1.5}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92}, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi{sub 1.657}Fe{sub 1.092}Nb{sub 1.150}O{sub 7} exhibited low-temperature dielectric relaxation similar to that observed for Bi{sub 1.5}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92}; at 1MHz and 200K the relative permittivity was 125, and above 350K conductive effects were observed.« less
  • The composition, dielectric properties and inherent displacive disorder of a Bi-based, misplaced-displacive cubic pyrochlore phase found in two ternary Bi{sub 2}O{sub 3} - M {sup 2+}O-Nb{sub 2}O{sub 5} (M=Ni and Mg) systems has been investigated. The dielectric permittivities (up to 1 MHz) of (Bi{sub 0.825}Ni{sub 0.125}{open_square}{sub 0.05}){sub 2}(Ni{sub 0.25}Nb{sub 0.75}){sub 2}O{sub 7} and (Bi{sub 0.835}Mg{sub 0.085}{open_square}{sub 0.08}){sub 2}(Mg{sub 0.235}Nb{sub 0.765}){sub 2}O{sub 7} at room temperature are found to be 116 and 151, respectively, while the dielectric loss tangents are 0.00065 and 0.00042, respectively, at 100 kHz. A highly structured characteristic diffuse intensity distribution apparent in electron diffraction is reported inmore » both cases and partially interpreted in terms of large amplitude, {beta}-cristobalite-type tetrahedral rotations of the O'A {sub 2} tetrahedral framework sub-structure of the ideal pyrochlore structure type. Bond valence sum calculations are used to investigate the local crystal chemistry responsible for this displacive disorder. - Graphical abstract: The characteristic {beta}-cristobalite-type displacive disorder of the O'A {sub 2} sub-structure (of the ideal pyrochlore structure type) drawn relative to the surrounding B {sub 2}O{sub 6} octahedral framework sub-structure and responsible for the observed structured diffuse intensity distribution in the Bi{sub 1.65}Ni{sub 0.75}Nb{sub 1.50}O{sub 7} and Bi{sub 1.67}Mg{sub 0.64}Nb{sub 1.53}O{sub 7} misplaced-displacive cubic pyrochlores.« less
  • Bismuth-rich phases in the Bi{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}, Bi{sub 2}O{sub 3}-Ta{sub 2}O{sub 5}, Bi{sub 2}O{sub 3}-MoO{sub 3} and Bi{sub 2}O{sub 3}-WO{sub 3} systems have been investigated using synchrotron X-ray diffraction (XRD) and electron diffraction (ED) to resolve outstanding problems concerning phase relationships, unit cells, and symmetry. A temperature-composition phase diagram for the Bi{sub 2}O{sub 3}-Nb{sub 2}O{sub 5} system is presented. Single-phase powder specimens have been prepared for most phases. A modulated structure approach has been applied to the characterization of phases, and space groups or superspace groups assigned. The most appropriate description (commensurate modulation, incommensurate modulation or superstructure) formore » the structure of each of the phases is discussed.« less
  • The low-phosphate part of the SiO/sub 2/-Al/sub 2/O/sub 3/-Fe/sub 2/O/sub 3/-RO-R/sub 2/O-P/sub 2/O/sub 5/ system (the system) was examined with a constant content for the sum of the akalis and alkaline earths and with different ratios. The x-ray amorphous state was checked with a diffractometer an the structures were examined by electron microscope using shadowed platinum-carbon replicas and IR spectroscopy. Replacing SiO/sub 2/ by P/sub 2/O/sub 5/ results in a heterogeneous structure; x-ray phase analysis showed that high-alkali compositions had microheterogeneosity due to crystals of phosphates.