Synthesis and characterization of niobium doped hexagonal tungsten bronze in the systems, CsxNbyW1-yO3

Samples of nominal compositions, Cs0.25Nb (y) W1-y O-3 and Cs0.3Nb (y) W1-y O-3 with 0.0 a parts per thousand currency sign y a parts per thousand currency sign 0.25 and 0.0 a parts per thousand currency sign y a parts per thousand currency sign 0.3 were synthesized using appropriate amounts of Cs2WO4, WO3 and WO2 in evacuated and closed silica glass tubes at 800 A degrees C. The polycrystalline products contain hexagonal shaped crystals of up to 15 mu m diameter as long as y a parts per thousand currency sign 0.15. X-ray powder patterns of the samples reveal the formation of hexagonal tungsten bronze (HTB-I) type phase with y < 0.1. A mixture of HTB-I and an analogous less reduced hexagonal tungsten bronze (HTB-II) type phase is seen when y a parts per thousand yen 0.1. HTB-II content increases with increasing y, revealing close similarity to bronzoid type phases when y = x. Results of SEM/EDX analysis also support a partial substitution of tungsten by niobium in the HTB-I type phase. Infrared absorption and optical reflectivity data shows the effect of increasing amount of non-metallic phase for y > 0.1 and the effect of counterdoping by Nb5+/W5+ substitution in the metallic HTB-I type phase for y a parts per thousand currency sign 0.1, respectively. Reinvestigations in the system Rb0.3Nb (y) W1-y O-3 (0.0 a parts per thousand currency sign y a parts per thousand currency sign 0.175) show similar results with increasing content of HTB-II type phase related with y.