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  • 1
    Electronic Resource
    Electronic Resource
    Structure of Spinel (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper reviews the crystal structure of compounds with the general formula AB2X4, which crystallize with the same atomic structure as the mineral spinel, MgAl2O4. Three degrees of freedom associated with the detailed atomic arrangements of spinels are considered here: (i) the lattice parameter, a; (ii) the anion parameter, u; and (iii) the cation inversion parameter, i. Oxide spinels are used as examples to explore the interrelationships between these parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02241.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ion-beam-induced spinel-to-rocksalt structural phase transformation in MgAl2O4 (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2556-2558 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An ion-beam-induced metastable phase in magnesium aluminate spinel (MgAl2O4) has been examined in detail using transmission electron microscopy. Single crystals of MgAl2O4 with (111) orientation were irradiated with 180-keV Ne+ ions at 120 K to fluences of 1016 and 1017/cm2. Selected-area electron diffraction patterns obtained from the irradiation-induced damaged layer revealed that all even hkl reflections (e.g., 222) possess strong intensity, while all odd hkl reflections (e.g., 111) are weak. The features of these diffraction patterns corresponded to those of the rocksalt (NaCl) structure, suggesting that an ordered spinel to disordered rocksalt structural phase transformation in MgAl2O4 was induced by ion beam irradiation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126406
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  • 3
    Electronic Resource
    Electronic Resource
    Structure and Electronic States of Defects in Spinel of Different Compositions MgO·nAl2O3:Me (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper reviews the nature of defects and optical centers in magnesium aluminate spinel. The identification of absorption and luminescence bands was used to investigate the influence of UV and electron irradiation on optical center formation. Crystals examined were nominally pure MgO-nAl2O3 crystals with compositions in the series n= 1.0, 1.5, 2.0, and 2.5. MgO·Al2O3 crystals doped with transition-metal ion dopants were also studied to determine the influence of impurities on the nature and concentration of lattice defects in spinel. Results strongly suggest that absorption bands at 3.78 and 4.15 eV, and luminescence bands near 5 eV, may be attributed to optical centers on antisite defects. It is also apparent that through the introduction of specific amounts of Mn and Cr ions, the concentration of optical centers (which are related to defects such as cation antisites in the spinel structure) can be considerably changed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02252.x
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  • 4
    Electronic Resource
    Electronic Resource
    Disorder in Pyrochlore Oxides (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Contour plots of disorder reaction energies across a wide variety of A2B2O7 pyrochlore oxides have been produced, using atomistic simulation calculations based on energy-minimization techniques. The cations studied range from Lu3+ to La3+ on the A site and from Ti4+ to Ce4+ on the B site. The present results relate the experimentally observed stability range of the pyrochlore structure to A and B cation size and disorder. Disorder enthalpies decrease dramatically with increasing B cation size, while the rate of increase with A cation size depends markedly on the particular B cation. The association of anion Frenkel and cation antisite disorders is found to be of importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01484.x
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  • 5
    Electronic Resource
    Electronic Resource
    Cation Disorder and Vacancy Distribution in Nonstoichiometric Magnesium Aluminate Spinel, MgO·xAl2O3 (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Neutron diffractometry and X-ray diffractometry were used to characterize the cation disorder and vacancy distribution in nonstoichiometric spinel, MgO·xAl2O3, where x greaterthan equal to 1.0. Both synthetic and natural samples were examined. Least-squares refinements of integrated intensities for single crystals and Rietveld profile refinements for powders yielded the average scattering “power” from tetrahedral and octahedral sites within the almost-perfect cubic close-packed oxygen sublattice. The cation disorder was calculated assuming models in which the vacancies resided on tetrahedral, octahedral, or both types of sites. No degree of cation disorder was consistent with the tetrahedral vacancy model, and vacancies most likely resided on octahedral sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02242.x
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