Title
A pseudo-tetragonal tungsten bronze superstructure : a combined solution of the crystal structure of <tex>$K_{6.4}(Nb,Ta)_{36.3}O_{94}$</tex> with advanced transmission electron microscopy and neutron diffraction A pseudo-tetragonal tungsten bronze superstructure : a combined solution of the crystal structure of <tex>$K_{6.4}(Nb,Ta)_{36.3}O_{94}$</tex> with advanced transmission electron microscopy and neutron diffraction
Author
Faculty/Department
Faculty of Sciences. Physics
Publication type
article
Publication
London ,
Subject
Physics
Chemistry
Source (journal)
Journal of the Chemical Society: Dalton transactions. - London
Volume/pages
45(2016) :3 , p. 973-979
ISSN
1477-9226
ISI
000367614700018
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
The crystal structure of the K6.4Nb28.2Ta8.1O94 pseudo-tetragonal tungsten bronze-type oxide was determined using a combination of X-ray powder diffraction, neutron diffraction and transmission electron microscopy techniques, including electron diffraction, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), annular bright field STEM (ABF-STEM) and energy-dispersive X-ray compositional mapping (STEM-EDX). The compound crystallizes in the space group Pbam with unit cell parameters a = 37.468(9) Å, b = 12.493(3) Å, c = 3.95333(15) Å. The structure consists of corner sharing (Nb,Ta)O6 octahedra forming trigonal, tetragonal and pentagonal tunnels. All tetragonal tunnels are occupied by K+ ions, while 1/3 of the pentagonal tunnels are preferentially occupied by Nb5+/Ta5+ and 2/3 are occupied by K+ in a regular pattern. A fractional substitution of K+ in the pentagonal tunnels by Nb5+/Ta5+ is suggested by the analysis of the HAADF-STEM images. In contrast to similar structures, such as K2Nb8O21, also parts of the trigonal tunnels are fractionally occupied by K+ cations.
E-info
https://repository.uantwerpen.be/docman/iruaauth/2b47c1/130408.pdf
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