ISSN:
1662-8985
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Crystal structures of SrAl2O4, BaAl2O4 and their solid solutions have been reviewed interms of the linkage pattern of [AlO4] tetrahedra. With SrAl2O4 the hexagonal-to-monoclinic phasetransformation occurs at 950K during cooling. The space group change from P63 to its subgroup P21eliminates the triad axis of the former phase, which involves a reduction in the symmetry of thetrigonally distorted rings. The hexagonal structures of SrAl2O4 and BaAl2O4 differ distinctly in thelinkage pattern of the [AlO4] tetrahedra. In the former structure, all of the tetrahedral rings areequivalent. In the latter, there are two types of tetrahedral rings; trigonal rings and asymmetrical ones.The trigonal rings, comprising 25% of the total number of rings, contain in their centers the Ba atomswith the special position. This implies that the triad axes exist in the centers of the rings, and hencethey are distorted trigonally as in the hexagonal SrAl2O4. On the other hand, the Ba atoms in theasymmetrical rings are located at the general position site. The structural disorder in Ba0.6Sr0.4Al2O4(space group P6322) was investigated by the combined use of Rietveld method and maximum-entropymethod. The electron density distribution was satisfactorily expressed by the split-atom model, inwhich the strontium/barium and oxygen atoms were split to occupy the lower symmetry sites
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/39/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.11-12.43.pdf
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