Complex Structures with Oxides of Mo, W, V, Nb, Ta, Ti

The well-known pigmentary bronzes, which are electrical conductors and show a range of colours, contain reduced forms of WO3. In these compounds, a limited number of are replaced by cations, but the total number of O atoms remains constant. In order to maintain charge balance, alkali metal cations can be introduced in the otherwise empty channels to stabilise the structure  

An example is Na W03, which is golden yellow when x = 0.9, red when x = 0.6 and deep violet when x= 0.3. 

FIGURE 5.43 Structure of WO3 (ReOj type), (a) Corner-shared octahedra (elevation) (b) structure in plan. 

FIGURE5.44 Structures of WOg octahedra and (a) PO4 or (b) P2O7 polyhedra (viewed end-on). 

Bronzes with lustre and metallic or semiconducting properties can be obtained not only with M = W, Mo or V, but in some cases with Ti, Ta, Nb or Ru. 

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