Studies of phases in the KNbO/sub 3/-Nb/sub 2/O/sub 5/ system by high-resolution electron microscopy and x-ray powder diffraction

Journal Article · Tue Jul 01 04:00:00 EDT 1986 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(86)90172-6· OSTI ID:5405726

Lundberg, M; Sundberg, M

High-resolution electron microscopy and x-ray powder diffraction studies of specimens in the KNbO/sub 3/-Nb/sub 2/O/sub 5/ system have shown that, besides the previously reported layer structures K/sub 4/Nb/sub 6/O/sub 17/ and L-KNb/sub 3/O/sub 8/, there exist three different types of tetragonal tungsten-bronze-related structures as well as a block structure, KNb/sub 13/O/sub 33/, isostructural with the NaNb/sub 13/O/sub 33/ phase. The parameters and the structural relations to TTB are discussed. The first two TTB-related phases, superstructures of the TTB-type, are characterized by the formula K/sub 2x/Nb/sub 2-x//sup A/(NbO)/sub x//sup C/Nb/sub 10/O/sub 30/, where 0 < x less than or equal to 2. H-KNb/sub 3/O/sub 8/ (x = 2), a high-temperature phase, exhibits a new mode of linking pentagonal columns in pairs. Various types of microstructures between the two TTB-related phases will be discussed. The third TTB-related phase can be described as K/sub 10-5y/Nb/sub y//sup A/Nb/sub 10/O/sub 30/, where 0.8 < y < 1.25. No pentagonal columns have so far been observed. In specimens prepared at T > 1275 K, the low-temperature modification L-KNb/sub 3/O/sub 8/, transforms in the solid state via a poorly crystallized phase to TTB-related structures. Some geometrical features of the L-KNb/sub 3/O/sub 8/, KNb/sub 13/O/sub 33/ structures and the TTB phase will also be presented.

• Research Organization: Univ. of Stockholm, Sweden
• OSTI ID: 5405726
• Journal Information: J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 63:2; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
&amp; Refractories-- Structure &amp; Phase Studies
ALKALI METAL COMPLEXES
CHALCOGENIDES
COHERENT SCATTERING
COMPLEXES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
DATA
DIFFRACTION
ELECTRON MICROSCOPY
EXPERIMENTAL DATA
INFORMATION
LATTICE PARAMETERS
MICROSCOPY
NIOBIUM COMPOUNDS
NIOBIUM OXIDES
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
POTASSIUM COMPLEXES
POWDERS
REFRACTORY METAL COMPOUNDS
SCATTERING
TETRAGONAL LATTICES
TRANSITION ELEMENT COMPOUNDS
X-RAY DIFFRACTION