High resolution electron microscopy study in the NaNbO sub 3 -Nb sub 2 O sub 5 -WO sub 3 system

Journal Article · Mon Jan 01 04:00:00 EST 1990 · Journal of Solid State Chemistry; (USA)

DOI:https://doi.org/10.1016/0022-4596(90)90181-V· OSTI ID:6623828

Sundberg, M; Marinder, B O ^[1]

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1. Univ. of Stockholm (Sweden)

High resolution electron microscopy studies have been made in the system NaNbO{sub 3}-Nb{sub 2}O{sub 5}-WO{sub 3} with emphasis on the following two lines in the phase diagram: Na{sub 2-x}M{sub 6}O{sub 16}, O < x < 2, and Na{sub 1.50-x}M{sub 6.1}O{sub 16}, O < x < 1.5, M = Nb, W. The presence of four structure types, three of which are related to the tetragonal tungsten bronze (TTB) type, has been revealed. The X-ray diffraction patterns only indicated a basic TTB structure in their region. The fourth one, observed in a sample of composition Na{sub 1.40} Nb{sub 6.12}O{sub 16}, is isotypic with NaNb{sub 6}O{sub 15}F. The most frequently observed TTB structure is of the Nb{sub 8}W{sub 9}O{sub 47} type, consisting of three basic TTB unit cells with four pentagonal columns (PCs) in the triple unit. The second most common phase type is NaNb{sub 5}WO{sub 16} isotypic with KNb{sub 12}O{sub 29}F{sub 3} (with a structure comprising two basic TTB unit cells, with four PCs in a square arrangement) which has a doubled content of alkali atoms. A third TTB-related structure observed in Na{sub 1.41}Nb{sub 6.01}W{sub 0.09}O{sub 16} is isotypic with KNb{sub 6}O{sub 15}F (with two basic TTB unit cells and with two PCs connected by a common octahedron). There are indications that an excess of transition metal stabilizes this phase as well as the NaNb{sub 6}O{sub 15}F type phase. Twinning, defects, and intergrowth of TTB-related phases are frequently observed phenomena.

• OSTI ID: 6623828
• Journal Information: Journal of Solid State Chemistry; (USA), Journal Name: Journal of Solid State Chemistry; (USA) Vol. 84:1; ISSN JSSCB; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
&amp; Refractories-- Structure &amp; Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400200 -- Inorganic
Organic
&amp; Physical Chemistry
ALLOYS
CHALCOGENIDES
COPPER ALLOYS
COPPER BASE ALLOYS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DATA
DATA ANALYSIS
ELECTRON MICROSCOPY
EXPERIMENTAL DATA
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
MICROSCOPY
NIOBIUM COMPOUNDS
NIOBIUM OXIDES
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
REFRACTORY METAL COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN ALLOYS
TUNGSTEN BRONZE
TUNGSTEN COMPOUNDS
TUNGSTEN OXIDES
TWINNING