Issue 3, 2016

A pseudo-tetragonal tungsten bronze superstructure: a combined solution of the crystal structure of K6.4(Nb,Ta)36.3O94 with advanced transmission electron microscopy and neutron diffraction

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.

Graphical abstract: A pseudo-tetragonal tungsten bronze superstructure: a combined solution of the crystal structure of K6.4(Nb,Ta)36.3O94 with advanced transmission electron microscopy and neutron diffraction

Supplementary files

Article information

Article type
Paper
Submitted
07 Sep 2015
Accepted
20 Nov 2015
First published
23 Nov 2015

Dalton Trans., 2016,45, 973-979

Author version available

A pseudo-tetragonal tungsten bronze superstructure: a combined solution of the crystal structure of K6.4(Nb,Ta)36.3O94 with advanced transmission electron microscopy and neutron diffraction

R. Paria Sena, A. A. Babaryk, S. Khainakov, S. Garcia-Granda, N. S. Slobodyanik, G. Van Tendeloo, A. M. Abakumov and J. Hadermann, Dalton Trans., 2016, 45, 973 DOI: 10.1039/C5DT03479E

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