US EPA

4834811 

Journal Article 

Tantalum and vanadium substitution in hexagonal K0.3WO3 bronze: synthesis and characterization 

Rahman, JerzyS; Murshed, AndrzejM; Baabe, D; Gesing, TM 

2016 

231 

1 

11-21 

10.1515/zkri-2015-0003 

WOS:000370945500002 

Polycrystalline samples of tantalum and vanadium single and double substituted hexagonal potassium tungsten bronzes (K-HTB's) with nominal compositions of K-0.3(W-0.7(6+) W0.3-y5+Tay5+)O-3 (0 <= y <= 0.3), K-0.3(W-0.7(6+) W0.3-y5+Tay5+)O-3 (0 <= y <= 0.18) and K-0.3(W-0.7(6+) W0.3-y5+Tay/25+Vy/25+ )O-3 (0 <= y <= 0.3), were synthesized by solid state reactions in quartz tubes at 10(-7) MPa and 1073 K. The applied synthesis condition allowed K0.3WO3 to crystallize in space group P6(3)22, confirmed by X-ray powder diffration and Raman spectroscopic analyses. In this K-HTB composition, W5+ could fully be replaced by Ta5+, whereas V5+ could only be substituted up to y = 0.16. The degree of W5+ substitution was explained in terms of second-order Jahn-Teller (SOJT) distortion of the d(0) cations W6+, Ta5+ and V5+. The applied distortion index also demonstrates why a complete substitution of W5+ in K-0.3(W6+ W5+)O-3 was allowed by a concomitant sharing of Ta5+ and V5+, which are statistically distributed on the W5+/W6+ sites. As W5+(d(1)) is not SOJT susceptible, it is also shown that the concentration of W5+ in tungsten bronzes plays an important role in the local WO6 octahedral symmetry as well as in its coordination. 

crystal structure; Jahn-Teller distortion; Raman spectroscopy; tungsten bronzes; X-ray diffraction