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  • American Ceramics Society  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    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: Native point defects in yttrium aluminum garnet (YAG) are studied in the framework of the pair-potential approximation, coupled with the shell-model description of the lattice ions. For the perfect lattice, a new set of potential parameters is obtained; these parameters reproduce the structure, elastic, and dielectric constants of YAG very well. The calculated formulation energies for native defects suggest that antisite disorder is preferred over Frenkel and Schottky-like disorder in YAG. The calculated values of the distortion that is caused by the antisite Y atom that substitutes in the Al site in the lattice are in excellent agreement with the extended X-ray absorption fine-structure (EXAFS) measurements. In nonstoichiometric YAG, the calculated reaction energies indicate that excess Y2O3 or Al2O3 most likely is accommodated by the formation of antisites, rather than vacancies, in the lattice.
    Type of Medium: Electronic Resource
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  • 2
    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: Stoichiometric zinc aluminate (ZnAl2O4) and zinc gallate (ZnGa2O4) are simulated in the framework of the shell model, for which a new set of two-body interatomic potential parameters has been developed. Using these parameters, a reasonable prediction is made for elastic and dielectric constants of ZnAl2O4 and ZnGa2O4. Both oxides are stable against decomposition to the component oxides. The fitting of the potential energy surface of these oxides to the equation of state yields the bulk modulus and its pressure derivative. The bulk modulus is predicted to be higher in ZnAl2O4 as compared with that in ZnGa2O4, whereas the pressure derivative remains the same in both oxides. On the other hand, the octahedral and tetrahedral volumes of ZnGa2O4 are greater than those of ZnAl2O4. These differences in compressibility behavior can be attributed to the size difference between Al3+ and Ga3+ in the spinel oxides considered here. The calculated formation energies of the native defects suggest the preference of disorder in the cation sublattice over the Schottky and Frenkel defects. Although the degree of disorder is expected to be small, it is likely to influence the vacancy population in the lattice. Finally, deviations from stoichiometry are considered in which a preference for the dissolution of Al2O3/Ga2O3 via the formation of zinc vacancies is predicted relative to that of ZnO in ZnAl2O4/ZnGa2O4.
    Type of Medium: Electronic Resource
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