Characterization of niobium substituted potassium tetragonal tungsten bronzes

Department of Chemistry, University of Dhaka
â—‹Subrata Chandra Roy Altaf Hussain

Tungsten bronzes,MxWO3, are well known non-stoichiometric ternary metal oxides where M is typically an electropositive metal and 0<x<1. Among tungsten bronzes, the alkali metal tungsten bronzes are extensively studied compounds. Fully oxidized, isostructural phases termed as bronzoids, MxNbyW1-yO3, and partially oxidized bronzes of alkali metals have also been reported.

In our present investigation, powder samples of potassium tetragonal tungsten bronzes (TTB), KxWO3 , and niobium substituted TTB, KxNbyW1-yO3, were prepared by the conventional solid-state method at 800oC. The powder samples were characterized by X-ray powder diffraction technique.

XRD patterns of K0.50WO3 and K0.55WO3 show TTB phase while the sample with composition K0.45WO3 shows a mixture of TTB and hexagonal tungsten bronzes (HTB) phases.

Attempts to substitute Nb in K0.45WO3 result mixtures of HTB and TTB phases and with y > 0.1 the TTB phase disappears giving rise to an orthorhombic phase along with HTB. While for the systems K0.50NbyW1-yO3 and K0.55NbyW1-yO3 a single phase of TTB is observed upto y = 0.05 and y = 0.07 respectively. Further substitution of Nb in these compositions results mixture of TTB and HTB phases.