Sodium tungsten bronze is a form of insertion compound with the formula NaxWO3, where x is equal to or less than 1. Named due to its metallic lustre, its electrical properties range from semiconducting to metallic depending on the concentration of sodium ions present; it can also exhibit superconductivity.

 

Prepared in 1823 by the chemist Friedrich Wöhler, sodium tungsten bronze was the first alkali metal bronze to be discovered. They owe some of their properties to the relative stability of the tungsten(V) cation that is formed. A similar family of molybdenum bronzes may have been discovered in 1885 by Alfred Stavenhagen and E. Engels, but they are formed in a very narrow range of temperatures and were not reported again until the 1960s.

 

The formation of the sodium tungsten bronzes (NaxWO3; 1 >= x > 0) from mixtures of sodium tungstate, tungsten(VI) oxide and tungsten has been studied in the temperature range 500-750°, where all of the reactants remain solid. Extremely long reaction times are required to effect complete reaction, which, as shown by X-ray studies, checked at a few points by chemical analysis, occurs only within the range from Na0.30WO3 to Na0.85WO3 under these reaction conditions. The end member of the series, NaWO3, cannot be prepared by this method, but a new value of about 3.866 A. is suggested for the lattice constant of this compound by extrapolation of the X-ray data from the region in which complete reaction has occurred.