Preprint
Article
On the Arrangement of Pentagonal Columns in Tetragonal Tungsten Bronze-Type Nb18W16O93
This version is not peer-reviewed.
Submitted:
11 November 2021
Posted:
12 November 2021
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Abstract
The evaluation of HAADF-STEM images of a sample with the composition Nb18W16O93 provided new insights in its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of the pentagonal tunnels (PT) by metal-oxygen strings determines the oxygen to metal ratio (O/SM with M = Nb,W). For a large area, the O/SM was determined to be 2.755 which is smaller than the value of Nb18W16O93 which is O/SM = 2. 735. To a large extent, the threefold TTB superstructure structure of Nb8W9O47 with a high oxygen content is present (O/SM = 2.765). In addition, a new fourfold TTB superstructure was found in small domains: Nb12W11O63 with an O/SM = 2.739 obviously accommodates a part of the sample’s metal excess compared to the stable phase Nb8W9O47.
Keywords:
niobium tungsten oxide
; pentagonal tunnels
; tetragonal tungsten bronze
; high-angle annular dark field detector
; scanning transmission electron microscopy
; HAADF-STEM
; twinning
; superstructure
; battery material.
Copyright: This open access article is published under a Creative Commons CC BY 4.0 license, which permit the free download, distribution, and reuse, provided that the author and preprint are cited in any reuse.
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