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Hexagonal Perovskite‐Type Phases in the BaO‐Rich Part of the BaO–WO 3 –Nb 2 O 5 System
Author(s) -
Bezjak Jana,
Jančar Boštjan,
Boullay Philippe,
Rečnik Aleksander,
Suvorov Danilo
Publication year - 2009
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2009.03299.x
Subject(s) - orthorhombic crystal system , crystallography , materials science , barium , crystallite , tungsten , x ray crystallography , crystal structure , solid solution , transmission electron microscopy , perovskite (structure) , niobium , analytical chemistry (journal) , chemistry , diffraction , nanotechnology , metallurgy , physics , chromatography , optics
BaO‐rich phases with the nominal compositions Ba 6 Nb x W 3− x O 15− x /2 ( x =1, 2), 9L‐Ba 9 Nb 2 W 4 O 26 , 12‐layered (12L)‐Ba 4 Nb 2 WO 12 , and 27L‐Ba 9 Nb 6 WO 27 were synthesized as polycrystalline powders using solid‐state techniques and characterized by X‐ray powder diffractometry and transmission electron microscopy. Of these powders only the 5L2‐Ba 6 Nb x W 3− x O 15− x /2 ( x =2) and 9L‐Ba 9 Nb 2 W 4 O 26 were obtained as single‐phase materials. The formation of Ba 6 Nb x W 3− x O 15− x /2 ( x =1, 2) started with the occurrence of binary compounds. Thus, 5L1‐Ba 6 Nb x W 3− x O 15− x /2 ( x =1) appeared over binary Ba 4 Nb 2 O 9 in contrast to 5L2‐Ba 6 Nb x W 3− x O 15− x /2 ( x =2), which formed through a reaction between Ba 5 Nb 4 O 15 and other barium–tungsten oxides. 5L2‐Ba 6 Nb x W 3− x O 15− x /2 ( x =2) appeared in two different polymorphs structurally related to the hexagonal Ba 6 Ta 2 WO 14 and the orthorhombic β‐Ba 4 Nb 2 O 9 . The structural refinement of the high‐temperature 5L2‐Ba 6 Nb x W 3− x O 15− x /2 ( x =2) was carried out using the space group P 3 m 1. The fitted parameters of the hexagonal unit cell corresponded to a H =6.030(1) Å and c H =12.44(1) Å. Additional reflections of variable intensity and strong, diffuse scattering in the electron diffraction patterns indicated a strong structural disorder. The formation of 9L‐Ba 9 Nb 2 W 4 O 26 , 12L‐Ba 4 Nb 2 WO 12 , and 27L‐Ba 9 Nb 6 WO 27 started with the reaction between the binary compounds and continued over a series of intermediate hexagonal perovskite‐type phases lying on the Ba 3 W 2 O 9 –Ba 5 Nb 4 O 15 tie line.