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Samples of nominal compositions, CsNbWO and CsNbWO with 0.0 ≤ y ≤ 0.25 and 0.0 ≤ y ≤ 0.3 were synthesized using appropriate amounts of CsWO, WO and WO in evacuated and closed silica glass tubes at 800 °C. The polycrystalline products contain hexagonal shaped crystals of up to 15 μm diameter as long as y ≤ 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 ≥ 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 Nb/W substitution in the metallic HTB-I type phase for y ≤ 0.1, respectively. Reinvestigations in the system RbNbWO (0.0 ≤ y ≤ 0.175) show similar results with increasing content of HTB-II type phase related with y. [ABSTRACT FROM AUTHOR]

Needle-shaped crystals of sizes up to 5 μm × 5 μm × 40 μm of nominal composition K x Nb y W1− y O3 were synthesized by solid state method at 800 °C using appropriate amount of WO3, WO2, Nb2O5, and K2WO4. The samples were characterized with XRD, SEM, microprobe analysis, optical spectroscopy, and Raman spectroscopy. The XRD patterns of the samples show single phase of tetragonal tungsten bronze (TTB) type (P4/mbm, No. 127) up to y = 0.07. Structure refinements reveal an increase in cell parameter with increasing nominal niobium content within the TTB phase. The elemental compositions of the crystals determined by electron microprobe analysis also show an increase in Nb content with increasing y. With increasing Nb content the reflectivity minimum in the near infrared spectral range shifts towards lower wavenumber indicating the effect of decreasing carrier concentration. Pyrochlore type phase (KNbWO6) is obtained as a second phase when nominal composition y > 0.07. [ABSTRACT FROM AUTHOR]

Needle-shaped crystals of sizes up to 5 μm × 5 μm × 40 μm of nominal composition K x Nb y W1− y O3 were synthesized by solid state method at 800 °C using appropriate amount of WO3, WO2, Nb2O5, and K2WO4. The samples were characterized with XRD, SEM, microprobe analysis, optical spectroscopy, and Raman spectroscopy. The XRD patterns of the samples show single phase of tetragonal tungsten bronze (TTB) type (P4/mbm, No. 127) up to y = 0.07. Structure refinements reveal an increase in cell parameter with increasing nominal niobium content within the TTB phase. The elemental compositions of the crystals determined by electron microprobe analysis also show an increase in Nb content with increasing y. With increasing Nb content the reflectivity minimum in the near infrared spectral range shifts towards lower wavenumber indicating the effect of decreasing carrier concentration. Pyrochlore type phase (KNbWO6) is obtained as a second phase when nominal composition y > 0.07. [ABSTRACT FROM AUTHOR]

Abstract: Series of compounds in the system Na x Nb y W1− y O3 were prepared according to the appropriate molar ratio of Na2WO4, WO3, WO2 and Nb2O5 with x=0.80 and 0.0⩽y⩽0.4 at 600°C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition Na x WO3 with slightly decreasing x (i.e. 0.8–0.72) with increasing nominal y, (ii) bluish solid solution of composition Na x Nb y W1− y O3 and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na0.5NbO2.75. [Copyright &y& Elsevier]