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

Abstract

Single crystal fibres with thickness >6 μm and length ∼3 mm were obtained by calcining the mixtures of natural topaz (Al 2SiO 4(F 0.75,(OH) 0.25) 2), tungsten trioxide (WO 3), and potassium tungstate (K 2WO 4). The single crystal fibres were characterised by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron probe microanalysis (EMPA). It was found that the fibres exhibited a hexagonal crystalline structure and possessed the nonstoichiometry of K 0.25WO 3.11. It was believed that the vapours of SiF 4, HF, and H 2O from the decomposition of the natural topaz were responsible for the chemical transport of the WO 3 and the K 2WO 4. The subsequent chemical reaction of the transported vapour species resulted in the formation of the hexagonal tungsten oxide bronze fibres.