Tetragonal tungsten bronzes

Known oxyfluoroniobates (-tantalates) with compositions that correspond to X Me = 3 crystallize in typical structures of ReC>3, pyrochlore, and hexagonal and tetragonal tungsten bronze. Table 35 presents structural parameters of such compounds. 

When 0.4 < x < 0.53, an orthorhombic phase is observed in the AgxNb02+xFi.x system. This phase undergoes a phase transition at 900°C that leads to the formation of a tetragonal phase, which crystallizes in a tetragonal tungsten bronze-type structure with cell parameters a = 12.343 and c = 3.905 A. When 0.82 < x < 1, solid solutions based on AgNb03 were found, which crystallize in a perovskite-type structure. 

Fig. 40. Structure of MxMe02+xF/.x type compounds — tetragonal tungsten bronze- type structure.

The second group is the group of oxyfluorides that are derived from ferroelectric oxides by means of fluorine-oxygen substitution. The basic oxides are usually perovskite, tetragonal tungsten bronze, pyrochlore, lithium tantalate etc. [400]. 

Linking of the octahedra in hexagonal and tetragonal tungsten bronzes M WOg. In the direction of view, the octahedra are arranged one on top of the other with common vertices. The channels in this direction contain varying amounts of alkali metal ions... 

Key words tetragonal tungsten bronze, charge ordering, electron diffraction... 

S.Fabbrici, E.Montanaii, G.Calestani and A. Migliori Charge ordering and tilt modulation in multiferroic KxM"xM "i xF3 (0.4transition metal fluorides with tetragonal tungsten bronze structure Chem. Mater. 2004 16(16) 3007-3019... 

Finally, a number of other mixed oxides that do not have the perovskite structure have also been examined. For example, niobium titanates with the rutile structure,tetragonal tungsten bronze... 

Figure 13 Projections of (a) tetragonal(II), and (b) hexagonal "tungsten bronze" structure. A polyhedral representation showing the large pentagonal and hexagonal tunnels, respectively. From Reference 55.

FIGURE 5.35 (a) The tetragonal tungsten bronze structure (b) the hexagonal tungsten bronze structure. The shaded squares represent WOe octahedra, which are linked to form pentagonal, square and hexagonal tunnels. These are able to contain a variable population of metal atoms, shown as open circles. 

Figure 1.16 Structure of the tetragonal tungsten bronze (TTB), K

A second example of the intergrowth structure is tungsten bronze, M,. WO3 (M = H, Li, Na, K, Rb, Cs, Ca, Sr, Ba, In, Tl, Ge, Sn, Pb, Cu, Ag etc. nowadays many bronzes such as Ti, V, Mo are well known ), so named because its colour is similar to that of alloy bronze CuZn. It has been shown to have a kind of intergrowth structure in a limited composition (x) range. Generally, the stability of the structural types (hexagonal, tetragonal, and cubic) depends both on the ionic radius (rj and the composition (x) of M. For instance,... 

Figure 9.1 Tetragonal tungsten-bronze structure of SiiBai-xNboOf, (Strontium barium nio-bate, SBN). Characteristic are the corner-linked niobium-oxygen-octahedra and 3 types of vacancies A,Bi,2,3 and C. Sr2+-ions are embedded in the A- and B2-positions and Ba2+ in the Bi-positions according to their ionic radii. The C-positions and B3-position remain empty.

---