Powder EPR study of natural cassiterites and synthetic Sn02 doped with Fe, Ti, Na and Nb
Ruck, Régine; Dusausoy, Yves; Nguyen Trung, Chinh; Gaite, Jean-Marie; Murciego, Ascension
European Journal of Mineralogy Volume 1 Number 3 (1989), p. 343 - 352
published: Jul 27, 1989
manuscript accepted: Feb 22, 1989
manuscript received: Oct 5, 1988
ArtNo. ESP147050103006, Price: 29.00 €
Abstract SnO2 powders were synthesized under hydrothermal conditions and doped at different temperatures with varying concentrations of Fe, Fe + Ti, Fe + Na and Fe + Nb in acidic solutions (HCl, HNO3, or HF). The paramagnetic centres were analyzed by EPR and then compared to the EPR spectra of natural cassiterites. The same Fe3+ centres (I and Sdl) are observed in synthetic SnO2 doped with Fe, Fe + Ti or Fe + Na in HCl solutions and in natural cassiterites (iron or iron and titanium rich). This is consistent with the charge compensation mechanism of the I centre (Fe3+-OH-). The Fe3+ concentration ratio in the I and Sdl centres always remains constant. The increase of niobium concentration in the growth medium involves an increase in the number of Sd2 centres and a progressive decrease of Sdl and I centres. A tenfold decrease in the Sdl and I centres and an approximately fivefold increase in the Sd2 centres was observed in the Fe and Nb-rich and coloured parts of a natural cassiterite in comparison to the Fe and Nb-poor and clearer parts. This is interpreted as the prior creation of Sd2 centres and FeNb2O6 phases at the expense of I and Sdl centres. The SN centre exists under very different conditions: HNO3 or HCl + HF solutions, containing Fe or Fe + Nb. It is not related to short or long distance Fe3+-Nb5+, Fe3+-Na+ or Fe3+-OH- coupling but the exact charge compensation mechanism is not yet clear.