Intermediate phases and pseudophases in the system WO/sub 3/--Nb/sub 2/O/sub 5/: tetragonal tungsten bronze phases

Journal Article · Sun Feb 01 04:00:00 EST 1976 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(76)90205-X· OSTI ID:7195594

Obayashi, H; Anderson, J S

Ordered intermediate phases with finely graded compositions are found in the Nb/sub 2/O/sub 5/--WO/sub 3/ system:homologous series of crystallographic shear phases for x in MO/sub x/(M = Nb + W) greater than 2.9; a succession of block structures and intergrowth structures for 2.5 less than or equal to x less than or equal to 2.65. The intermediate range has pentagonal tunnel structures partly based on the tetragonal tungsten bronze network. Ordered filling of some rational but variable, fraction of tunnel sites, in principle, could generate a new closely graded series of phases. Synthetic experiments and lattice imaging electron microscopy have been applied to this system. At least for the experimental conditions employed, the structure of the congruently melting 4Nb/sub 2/O/sub 5/.9WO/sub 3/, with 4/12 of pentagonal tunnels occupied, dominates the stability field. However, structures with 6/16 sites in a 2 x 2 TTB superlattice, and with 7/20 sites in a 5 x 1 TTB superlattice occupied form quite extended domains in a 4Nb/sub 2/O/sub 5/.9WO/sub 3/ matrix. In addition, the structure with 5/16 sites in a 2 x 2 TTB superlattice forms domains in preparations richer in WO/sub 3/ than 4Nb/sub 2/O/sub 5/.9WO/sub 3/, and this 2Nb/sub 2/O/sub 5/.5WO/sub 3/ structure itself shows evidence of ordered intergrowth with the 2NB/sub 2/O/sub 5/.7WO/sub 3/ characterized electron microscopically by Iijima. The status of these ordered domain structures is discussed. Metastable structures may be effectively stabilized by coherent intergrowth with structures that are absolutely stable.

• Research Organization: Oxford Univ.
• OSTI ID: 7195594
• Journal Information: J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 17:1-2; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
BINARY MIXTURES
CHALCOGENIDES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIAGRAMS
DISPERSIONS
DOMAIN STRUCTURE
ELECTRON MICROSCOPY
MICROSCOPY
MIXTURES
NIOBIUM COMPOUNDS
NIOBIUM OXIDES
OXIDES
OXYGEN COMPOUNDS
PHASE DIAGRAMS
SUPERLATTICES
TETRAGONAL LATTICES
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
TUNGSTEN OXIDES