Chemical order and local structure of the lead-free relaxor ferroelectric Na sub(1/2Bi) sub(1)/2TiO sub(3)

The A-site mixed perovskite sodium bismuth titanate (Na sub(1/2Bi) sub(1)/2)TiO sub(3 (NBT) is investigated by means of first-principles calculations based on density functional theory. By studying different geometries with varying occupations of the A-site, the influence of chemical order on the th...

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Bibliographic Details
Published in:Journal of solid state chemistry 2011-08, Vol.184 (8), p.2041-2046
Main Authors: Groeting, Melanie, Hayn, Silke, Albe, Karsten
Format: Article
Language:English
Subjects:
Bismuth titanate
Mathematical analysis
Nanostructure
Nucleation
Order disorder
Relaxors
Sodium
Stability
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Summary:The A-site mixed perovskite sodium bismuth titanate (Na sub(1/2Bi) sub(1)/2)TiO sub(3 (NBT) is investigated by means of first-principles calculations based on density functional theory. By studying different geometries with varying occupations of the A-site, the influence of chemical order on the thermodynamic stability and local structure is explored. We find that the hybridization of Bi 6sp with O 2p-states leads to stereochemically active Bi) super(3)+ lone pairs and increases the stability of structures with high Bi concentrations in {001}-planes. This goes along with displacive disorder on the oxygen sublattice, which up to now has been neglected in experimental studies. The calculated ordering energies are, however, small as compared to the thermal energy and therefore only short-range chemical order can be expected in experiments. Thus, it is conceivable that chemically ordered local areas can act as nucleation sites for polar nano-regions, which would explain the experimentally observed relaxor behavior of NBT.
ISSN:0022-4596
DOI:10.1016/j.jssc.2011.05.044