A study of the absorption spectra between 3350 and 12,500 A. has been made by diffuse reflectance methods, and the absorption peak wave length shows a linear shift to shorter wave lengths with increasing sodium content over the range where a single cubic phase is present. Single crystals, up to 12 mm. on an edge, have been grown by cathodic reduction of tungstate melts.

 

Since the first reported preparation of the sodium tungsten bronzes by Wohler, using hydrogen reduction of a sodium tungstate melt, this material has been prepared with tin, zinc, iron or phosphorus as the reducing agent, or by an electrolytic reduction of molten sodium tungstate-tungsten(VI) oxide solutions. These methods, however, did not yield a product whose composition could be predetermined.

 

More recently, Straumanis reported a preparation of these materials from a melt of sodium tungstate and tungsten(V1) oxide, using tungsten metal as the reducing agent. This reaction is based on the equation