Tungsten bronze-type structure

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.

LiNbC>3 type crystals and compounds that crystallize in a tungsten bronze-type structure. 

Strontium barium niobate is a single-crystal material with the tungsten bronze type of structure which is made by the Czochralski method but has yet to find a major use. It has relaxor characteristics of the type shown in Fig. 7.1 which give it a high pyroelectric coefficient and detectivity, but its high permittivity lowers the figure of merit l. ... 

Figure 31 (a) Electron micrograph of a crystal of an intergrowth tungsten bronze phase in the K.WOa system. The structure consists of slabs of WOs-like structure five octahedra wide separated by strips of the hexagonal tungsten bronze type, (b) A drawing of the idealized structure of the crystal in (a)... 

From the topological standpoint the Re03 structure is the simplest 3D framework structure for a compound AX3 built of octahedral AXe groups, for it is based on the simplest 3D 6-connected net. More complicated structures of the same general type are known, that is, structures in which every octahedron is joined to six others through their vertices. The tungsten bronzes have structures of this kind... 

Alkali tungsten bronzes of the type M WOs, M = K, Rb, or Cs with 0.16 < x 0.3 may adopt the hexagonal tungsten bronze (HTB) structure in which the large Cs atoms reside in hexagonal tunnels formed by six WOg octahedra in 12-fold coordination. The limit of x, as determined by the structure is 1/3. The structure is of interest since these compounds display superconductivity with values between 1 and 7K. It is also found for several mixed oxides of Nb and Ta with large A cations. 

Tungsten Bronze-Type Family Ba2NaNb 0i (BNN) (LB Ni/mhcr 66-o7j. This crystal is ferroelectric below about 580 °C. The crystal structure is modulated below 300 °C. This material is utilized for optical second-harmonic generation and in optical parametric osdllators (Fig. 4.5-38). 

Rubidium Chromium Fluoride Structures of the Hexagonal Tungsten Bronze Type, R. Sharma andL. Eyring, Ultramicroscopy, 22, 81-88 (1987). 

M. Leblanc, G. Ferey, P. Chevallier, Y. Calage, R. De Pape, Hexagonal tungsten bronze-type Fe" fluoride - (H20)o.33FeF3 - crystal-structure, magnetic-properties, dehydration to a new form of iron trifluoride, J. Solid State Chem., 47, 53-58 (1983). 

---