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  • Walter de Gruyter GmbH  (5)
  • 1
    Online Resource
    Online Resource
    Influence of the Bi 6 s 2 lone electron pair on elastic properties of monoclinic Bi 4 B 2 O 9
    Walter de Gruyter GmbH ; 2015
    In:  Zeitschrift für Kristallographie - Crystalline Materials Vol. 230, No. 11 ( 2015-11-1), p. 667-676
    Details
    In: Zeitschrift für Kristallographie - Crystalline Materials, Walter de Gruyter GmbH, Vol. 230, No. 11 ( 2015-11-1), p. 667-676
    Abstract: The coefficients of thermal expansion and the complete set of elastic stiffness coefficients of monoclinic Bi 4 B 2 O 9 were determined as functions of temperature employing dilatometry and, respectively, a combination of resonant ultrasound spectroscopy and the plate resonance technique. Thermal expansion as well as elasticity of Bi 4 B 2 O 9 exhibit a pronounced anisotropy, with the directions of the maximum longitudinal elastic stiffness and of the minimal longitudinal thermal expansion running almost parallel to [1̅02]. Further, between 100 K and 535 K the principal axes system of the linear thermal expansion rotates by more than 30° around the 2-fold symmetry axis. The deviations from Cauchy-relations show a similar behavior. Both, the anisotropy and the temperature induced changes of the investigated properties are mainly controlled by the stereochemically active Bi 6 s 2 lone electron pairs. At room temperature their Wang–Liebau vectors possess preferred components within a plane that runs almost perpendicular to [1̅02]. A systematic analysis of the elastic behavior of bismuth oxides using the quasi-additivity rule for elastic S -factor reveals a general trend: With decreasing relative amount of Bi 2 O 3 the Bi 3+ cations tend to align their stereochemically active lone electron pairs in planes or eventually in one direction. With respect to the elastic behavior of the compound the alignment of the easliy deformable lone electron pairs is unfavorable and causes an elastic softening.
    Type of Medium: Online Resource
    ISSN: 2196-7105 , 2194-4946
    URL: Article
    DOI: 10.1515/zkri-2015-1852
    RVK:
    VA 8180
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2015
    SSG: 13
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  • 2
    Online Resource
    Online Resource
    “Forbidden” reflections in neutron diffraction on bismuth metal oxides: symmetry reduction, λ/2 effect or Umweganregung?
    Walter de Gruyter GmbH ; 2013
    In:  Zeitschrift für Kristallographie - Crystalline Materials Vol. 228, No. 12 ( 2013-01)
    Details
    In: Zeitschrift für Kristallographie - Crystalline Materials, Walter de Gruyter GmbH, Vol. 228, No. 12 ( 2013-01)
    Type of Medium: Online Resource
    ISSN: 2196-7105 , 2194-4946
    URL: Article
    DOI: 10.1524/zkri.2013.1649
    RVK:
    VA 8180
    Language: Unknown
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2013
    SSG: 13
    Location Call Number Limitation Availability
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  • 3
    Online Resource
    Online Resource
    Single crystal growth and characterization of mullite-type Bi 2 Mn 4 O 10
    Walter de Gruyter GmbH ; 2012
    In:  International Journal of Materials Research Vol. 103, No. 4 ( 2012-04-01), p. 449-455
    Details
    In: International Journal of Materials Research, Walter de Gruyter GmbH, Vol. 103, No. 4 ( 2012-04-01), p. 449-455
    Abstract: A part of the pseudo-binary join Bi 2 O 3 –Bi 2 Mn 4 O 10 of the ternary system Bi 2 O 3 –MnO–MnO 2 was examined using thermo-analytical methods. Because Bi 2 Mn 4 O 10 melts incongruently single crystals of up to 20mm in diameter were grown by the top seeded solution growth method in the temperature range from about 1223K to 1173K. Single crystal neutron diffraction confirmed the principles of the crystal structure of Bi 2 Mn 4 O 10 but revealed much smaller distortions of the cation coordination polyhedra. In contrast to the anisotropy observed in other mullite-type Bi containing compounds, the linear thermal expansion of Bi 2 Mn 4 O 10 , as studied by means of dilatometry and X-ray powder diffraction techniques, is characterized by α 11 〉 α 33 〉 α 22 at room temperature. The relatively large expansion along the a -axis can be attributed to the two oxygen atoms bridging two corner shared MnO 5 tetrahedral pyramids which alternate with the structural void between two adjacent Bi 3 + cations.
    Type of Medium: Online Resource
    ISSN: 2195-8556 , 1862-5282
    URL: Article
    DOI: 10.3139/146.110714
    RVK:
    ZG 1100
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2012
    detail.hit.zdb_id: 2232675-3
    detail.hit.zdb_id: 2128058-7
    detail.hit.zdb_id: 203021-4
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  • 4
    Online Resource
    Online Resource
    Thermal expansion and elastic properties of mullite-type Bi 2 Ga 4 O 9 and Bi 2 Fe 4 O 9 single crystals
    Walter de Gruyter GmbH ; 2012
    In:  International Journal of Materials Research Vol. 103, No. 4 ( 2012-04-01), p. 438-448
    Details
    In: International Journal of Materials Research, Walter de Gruyter GmbH, Vol. 103, No. 4 ( 2012-04-01), p. 438-448
    Abstract: Resonant ultrasound spectroscopy was used to characterize the elastic properties of single crystal orthorhombic Bi 2 Ga 4 O 9 and Bi 2 Fe 4 O 9 between room temperature and about 1200 K. Additionally, the coefficients of thermal expansion were studied in the range 100 K to 1280 K using high-resolution dilatometry and X-ray powder diffraction. The elastic constants at 295 K are in GPa c 11 = 143.4(1), c 22 = 161.9(1), c 33 = 224.5(1), c 44 = 68.4(1), c 55 = 49.3(1), c 66 = 76.6(1), c 12 = 74.2(1), c 13 = 62.2(1), c 23 = 70.5(1) for Bi 2 Ga 4 O 9 , and c 11 = 106.7(1), c 22 = 141.2(1), c 33 = 183.7(2), c 44 = 53.7(1), c 55 = 41.9(1), c 66 = 63.8(1), c 12 = 63.5(1), c 13 = 59.8(1), c 23 = 63.4(2) for Bi 2 Fe 4 O 9 . In both mullite-type compounds the strong bond chains built up by edge-sharing coordination octahedra extending parallel to [001] dominate the anisotropy of their elastic and thermoelastic properties. Smaller variations of elastic anisotropy within the (001) plane can be attributed to the specific type of cross-linking of the octahedral chains. The temperature evolution of the c ij shows no hint on any structural instability or glass-like transition that might be related to the suspected ion conductivity at high temperatures. However, in both crystal species characteristic anelastic relaxation phenomena occur in the ultrasonic frequency regime close to room temperature. The smallest thermal expansion is observed in the plane perpendicular to the stiffest octahedral chains. A model is discussed to explain the apparent discrepancy in terms of cross-correlations within the three-dimensional framework of edge- and corner-linked coordination polyhedra.
    Type of Medium: Online Resource
    ISSN: 2195-8556 , 1862-5282
    URL: Article
    DOI: 10.3139/146.110718
    RVK:
    ZG 1100
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2012
    detail.hit.zdb_id: 2232675-3
    detail.hit.zdb_id: 2128058-7
    detail.hit.zdb_id: 203021-4
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  • 5
    Online Resource
    Online Resource
    Crystal chemistry and properties of mullite-type Bi 2 M 4 O 9 : An overview
    Walter de Gruyter GmbH ; 2012
    In:  International Journal of Materials Research Vol. 103, No. 4 ( 2012-04-01), p. 422-429
    Details
    In: International Journal of Materials Research, Walter de Gruyter GmbH, Vol. 103, No. 4 ( 2012-04-01), p. 422-429
    Abstract: Bi 2 M 4 O 9 ( M = Al 3+ , Ga 3+ , Fe 3+ ) belongs to the family of mullite-type crystal structures. The phases are orthorhombic with the space group Pbam. The backbones of the isostructural phases are edge-connected, mullite-type octahedral chains. The octahedral chains are linked by dimers of M 2 O 7 tetrahedral groups and by BiO polyhedra. The Bi 3+ cations in Bi 2 M 4 O 9 contain stereo-chemically active 6s 2 lone electron pairs (LEPs) which are essential for the stabilization of the structure. Although the octahedral chains of the closely related Bi 2 Mn 4 O 10 are similar to those of Bi 2 M 4 O 9 , Bi 2 Mn 4 O 10 contains dimers of edge-connected, five-fold coordinated pyramids instead of four-fold coordinated tetrahedra. Also the 6s 2 LEPs of Bi 3+ in Bi 2 Mn 4 O 10 are not stereo-chemically active. Complete and continuous solid solutions exist for Bi 2 (Al 1 – x Fe x ) 4 O 9 and Bi 2 (Ga 1 – x Fe x ) 4 O 9 ( x = 0–1). Things are more complex in the case of the Bi 2 (Fe 1 – x Mn x ) 4 O 9+ y mixed crystals, where a miscibility gap occurs between x = 0.25–0.75. In the Fe-rich mixed crystals most Mn atoms enter the octahedra as Mn 4+ , with part of the tetrahedral dimers being replaced by fivefold coordinated polyhedra, whereas in the Mn-rich compound Fe 3+ favorably replaces Mn 3+ in the pyramids. The crystal structure of Bi 2 M 4 O 9 directly controls its mechanical properties. The stiffnesses of phases are highest parallel to the strongly bonded octahedral chains running parallel to the crystallographic c -axis. Perpendicular to the octahedral chains little anisotropy is observed. The temperature-induced expansion perpendicular to the octahedral chains is probably superimposed by contractions. As a result the c -axis expansion appears as relatively high and does not display its lowest value parallel to c , as could be inferred. Maximally 6% of Bi 3+ is substituted by Sr 2+ in Bi 2 Al 4 O 9 corresponding to a composition of (Bi 0.94 Sr 0.06 ) 2 Al 4 O 8.94 . Sr 2+ for Bi 3+ substitution is probably associated with formation of vacancies of oxygen atoms bridging the tetrahedral dimers. Hopping of oxygen atoms towards the vacancies should strongly enhance the oxygen conductivity. Actually the conductivity is rather low ( σ = 7 · 10 − 2 S m − 1 at 1073 K, 800°C). An explanation could be the low thermal stability of Sr-doped Bi 2 Al 4 O 9 , especially in coexistence with liquid Bi 2 O 3 . Therefore, Bi 2 Al 4 O 9 single crystals and polycrystalline ceramics both with significant amounts of M 2+ doping ( M = Ca 2+ , Sr 2+ ) have not been produced yet. Thus the question whether or not M 2+ -doped Bi 2 M 4 O 9 is an oxygen conducting material is still open.
    Type of Medium: Online Resource
    ISSN: 2195-8556 , 1862-5282
    URL: Article
    DOI: 10.3139/146.110716
    RVK:
    ZG 1100
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2012
    detail.hit.zdb_id: 2232675-3
    detail.hit.zdb_id: 2128058-7
    detail.hit.zdb_id: 203021-4
    Location Call Number Limitation Availability
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