Tungsten bronze

Tungsten bronzes are oxidic compounds of tungsten with the general formula M _x WO _n (W = tungsten, M must be a mono-, di- or trivalent element), which are produced, among other things, by the reduction of tungsten (VI) oxide (WO ₃ ) . The tungsten is present in oxidation states +6 and +5 at the same time. The empirical formula M _x WO ₃ does not reflect that the tungsten bronzes are complicated non-stoichiometric compounds with ilmenite isotype phases . The term " bronze " comes from its physical properties; they have a metallic sheen and, depending on the M metal content, are electrically conductive or semiconducting .

For example, sodium bronzes are only electrical conductors from x> 0.25. Depending on the content x, the bronzes have a characteristic color. For sodium bronzes with small Na contents ranging from blue-black to red and orange to golden yellow. Tungsten bronzes with a sodium content of 0.3 <x <0.9 crystallize in the cubic perovskite type .

Alkali tungsten bronzes can generally be produced by solid-state reaction of alkali-containing tungstate with WO ₃ and tungsten .

Example sodium tungsten bronze:

${\displaystyle \mathrm {x/2Na_{2}WO_{4}+(3-2x)/3WO_{3}+x/6W\longrightarrow Na_{x}WO_{3}} }$

There are other bronzes with other alkali and alkaline earth metals , with transition metals , rare earths and analogous bronzes of molybdenum . There are also compounds containing alkali and alkaline earth metals that do not contain tungsten and are only named tungsten bronze after the structure type. Examples of this would be SrNb ₂ O ₆ , Ca ₂ NaNb ₅ O ₁₅ , K ₃ Li ₂ Nb ₅ O ₁₅ .

Individual evidence

1. ^ Leopold Gmelin; Gmelin handbook of inorganic chemistry
2. ↑ Lesley Smart, Elaine Moore; Introduction to Solid State Chemistry p. 185; ISBN 978-3540670667
3. ↑ Erwin Riedel ; Inorganic Chemistry p. 800; ISBN 978-3110181685