ISSN:
1573-8663
Keywords:
β′′-alumina
;
atomistic simulation
;
Nd3+
;
distribution
;
conduction plane
Source:
Springer Online Journal Archives 1860-2000
Topics:
Electrical Engineering, Measurement and Control Technology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract β′′-aluminas doped with Nd3+, in bothstoichiometric (Na2MgAl10O17) andnon-stoichiometric(Na1.66Mg0.66Al10.33O17) forms, have been studied through atomistic computer simulation. Theoptimum distribution of Mg2+ in the spinel blocks,Na+ as well as Nd3+ in the conduction planeshave been calculated and discussed in comparison with the structure modelsderived experimentally. Mg3+ ions prefer to occupy thetetrahedral Al(2) sites in the spinel blocks, and show strong tendency toform two- or three-membered clusters. Due to the presence ofMg2+, oxygen ions in or adjacent to the conduction plane,O(5), O(4) and O(3), are displaced from their ideal sites, leading to theremoval of the local symmetry at the mO site in parentβ′′-alumina. Doped Nd3+ ions are calculatedto be preferentially located in the vicinity of the mO sites (9d) and theirdisplacement from the ideal mO site is strongly affected by the distributionof Mg2+ and nearby Na+ vacancy. The bridgingoxygen in the conduction plane, O(5), relaxes off its original positiontowards the Nd3+ ions by ∼0.39AÅ, which is inexcellent agreement with previous X-ray diffraction and EXAFS studies. Theoxygen ions in the spinel block, O(3) and (4), are attracted towardsNd3+ non-uniformly, whereas the nearest Al(6c) ions aredisplaced in the opposite direction. The picture for the local structureclearly shows that the inversion symmetry at the Nd3+ positionis absent, due to the non-uniform displacement of surrounding oxygen atomsfrom their ideal positions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1009932918451
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