Authors: Tapas Debnath Subrata Chandra Roy Claus H Rüscher Altaf Hussain
Publish Date: 2009/01/01
Volume: 44, Issue: 1, Pages: 179-185
Abstract
Needleshaped crystals of sizes up to 5 μm × 5 μm × 40 μm of nominal composition KxNbyW1−yO3 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 = 007 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 007AH is grateful to the Alexander von Humboldt Stiftung Germany and University Grants Commission Bangladesh for financial support TD thanks the “Land Niedersachsen” Germany for support with the “Lichtenberg Stipendium” for his PhD research fellowship Finally the authors are thankful to two anonymous referees for their helpful comments
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