Tungsten bronze, hexagonal

The compound K0 3NbF3 has an average niobium valency of 2.7 and forms a crystal structure that is referred to as hexagonal tungsten bronze [239]. 

Abbreviations CC=cluster connectivity Of=overall framework HTB=hexagonal tungsten bronze HLF = Honeycomb-like layered framework [Tl5(Tl2Cl5)][(Nb6Cli204)3(Ti3CU)2]. 

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 1.15 The hexagonal tungsten bronze (HTB), Kq 33WO3 (projection onto the (001) plane). Notice the small triangular tunnels surrounding the big hexagonal tunnels. [Following Magneli (1953)].

Fig. 2.91 Structure of hexagonal tungsten bronze (HTB) M WOs. A group of six WOg forms tunnels of hexagonal prisms by sharing corners. This structure is composed of the structural elements A ( = B) and E, as shown by the arrows. Metal sites (open circles) are randomly and partially occupied.

M = V. Cr. Fe. Ga. Ti. Nb. or W X = F or F + O x = 0.35—0.55 0 < y < 1) have been obtained by heating mixtures of the corresponding fluorides and oxides. These materials all crystallize with the hexagonal tungsten bronze structure and their lattice constants have been determined.98... 

A good deal of work is still required to clarify the tetragonal and hexagonal tungsten bronze structures for which only the metal positions are known (32, 34). Superstructures of both have been observed, but little is known about them except in the case of the hexagonal phase at the composition BOs, where they are due to the ordering of molybdenum, an impurity substituent for tungsten (26). 

The conductivity of H—NiF3 is roughly 1 x 10 6(f).cm) 1 in contrast ofR—NiF3 which is an insulator [47], It is assumed that the conductivity associated with H—NiF3 is due to mobility of the K+ ions in the lattice of the hexagonal tungsten bronze structure. 

CN=coordination number fee = face-centered cubic hep = hexagonal close packing HTB = hexagonal tungsten bronze r.t. = room temperature s.g. = space group, TTB = tetragonal tungsten bronze. 

Dynamic Random Access Memory FeRAM = Ferroelectric Random Access Memory HCP = Hexagonal close packed HREM = High-resolution electron microscopy HTB = Hexagonal tungsten bronze MPTBh = Monophosphate tungsten bronzes with hexagonal tunnels MPTBp =... 

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) stmcture in which the large Cs atoms reside in hexagonal tunnels formed by six WOe octahedra in 12-fold coordination. The limit of x, as determined by the stmcture is 1/3. The stmcture 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. 

Figure 16 Normal perovskite layer. Circles represent A cations (a). Tetragonal trmgsten bronze layer (b). Hexagonal tungsten bronze layer...

A homologous series of cesium tungsten oxides having the formula Cs2 W4 iOi2 has been reported. The general stmcture consists of slabs composed of layers of the hexagonal tungsten bronze and the pyrochlore type. The alkali cations reside in between the layers and in the tunnels formed within the slabs. ... 

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