Synthesis and characterization of niobium substituted hexagonal tungsten bronzes

Alkali metal tungsten bronzes, MxWO3, and its niobium. substituted forms, MxNbyWi-yO3 have been prepared with M = K and Rb and nominal compositions of x, = 0.20, 0.25, 0.30 and 0.0 less than or equal to y less than or equal to 0.20 at temperatures between 600 and 900degreesC. The X-ray powder patterns reveal that single phases of niobium substituted hexagonal tungsten bronze (HTB) can be prepared for x = 0.2, y less than or equal to 0.05; x = 0.25, y less than or equal to 0.125 and x = 0.3, y less than or equal to 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.