GROWTH AND MORPHOLOGY OF W18O49 CRYSTALS PRODUCED BY MICROWAVE DECOMPOSITION OF AMMONIUM PARATUNGSTATE

By microwave irradiation of ammonium paratungstate (APT, (NH4)(10)H2W1 2O42. 4H(2)O), needle crystals of W18O49 with a wide variety of size a nd morphology were formed. Their sizes and morphologies varied dependi ng on various facets of individual APT pseudomorphous particles on whi ch whiskers were grown, and among neighbouring decomposed APT pseudomo rphous particles. Based on scanning electron and transmission electron -microscopic observations, it has been concluded that individual whisk ers were monocrystalline and grew by a root growth mechanism from a nu cleus formed in the amorphous layer, and that a rapid leader-like whis ker growth in length was followed by a subsequent slower growth in thi ckness. Any evidence supporting a screw dislocation mechanism or tip g rowth by vapour-liquid-solid have not been detected.