Abstract: | Alkali metal tungsten bronzes, MxWO3, and its niobium substituted forms, MxNbyW1‐yO3, have been prepared with M = K and Rb and nominal compositions of x = 0.20, 0.25, 0.30 and 0.0 ≤ y ≤ 0.20 at temperatures between 600 and 900?C. The X‐ray powder patterns reveal that single phases of niobium substituted hexagonal tungsten bronze (HTB) can be prepared for x = 0.2, y ≤ 0.05 ; x = 0.25, y ≤ 0.125 and x = 0.3, y ≤ 0.15. Investigations of the optical reflectivity and the infrared absorption of Rb0.3NbyW1‐yO3 indicate a decreasing concentration of free carrier with increasing niobium content. |