Tungsten bronze barium neodymium titanate (Ba6–3nNd8+2nTi18O54): an intrinsic nanostructured material and its defect distribution

Azough, F. et al. (2016) Tungsten bronze barium neodymium titanate (Ba6–3nNd8+2nTi18O54): an intrinsic nanostructured material and its defect distribution. Inorganic Chemistry, 55(7), pp. 3338-3350. (doi:10.1021/acs.inorgchem.5b02594) (PMID:26998674)

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Abstract

We investigated the structure of the tungsten bronze barium neodymium titanates Ba6–3nNd8+2nTi18O54, which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba6–3nNd8+2nTi18O54 (n = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the b lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba6–3nNd8+2nTi18O54 “perovskite” superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Schaffer, Dr Bernhard and MacLaren, Dr Ian
Authors: Azough, F., Cernik, R. J., Schaffer, B., Kepaptsoglou, D., Ramasse, Q. M., Bigatti, M., Ali, A., MacLaren, I., Barthel, J., Molinari, M., Baran, J. D., Parker, S. C., and Freer, R.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Inorganic Chemistry
Publisher:American Chemical Society
ISSN:0020-1669
ISSN (Online):1520-510X
Copyright Holders:Copyright © 2016 American Chemical Society
First Published:First published in Inorganic Chemistry 55(7): 3338-3350
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
413371SuperSTEM - the UK aberration corrected STEM facilityAlan CravenEngineering & Physical Sciences Research Council (EPSRC)EP/D040205/1P&A - PHYSICS & ASTRONOMY