Use of natural topaz as a transporting agent in the vapor growth of potassium tungsten oxide bronze fibres

Single crystal fibres with thickness >6 mu m and length similar to 3 mm wer e obtained by calcining the mixtures of natural topaz (Al2SiO4(F-0.75,(OH)( 0.25))(2)) tungsten trioxide (WO3), and potassium tungstate (K2WO4). The si ngle crystal fibres were characterised by scanning electron microscopy (SEM ), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and elect ron probe microanalysis (EMPA). It was found that the fibres exhibited a he xagonal crystalline structure and possessed the nonstoichiometry of K0.25WO 3.11 It was believed that the vapours of SiF4, HF, and H2O from the decompo sition of the natural topaz were responsible for the chemical transport of the WO3 and the K2WO4. The subsequent chemical reaction of the transported vapour species resulted in the formation of the hexagonal tungsten oxide br onze fibres. (C) 1999 Elsevier Science B.V. All rights reserved.