Acicular crystals of sodium tungsten bronzes

Abstract

The synthesis of sodium tungsten bronzes, Na x WO 3, with emphasis on crystals with acicular morphology, has been examined experimentally. The acicular morphology is obtained for a range of compositions in which 0.15≤ x≤0.28, and generally more than one crystal structure is present. At x≈0.28 the tetragonal II phase predominates, whereas at x≈0.15 an unknown structure is the major phase. Surprisingly, all the bronzes tested exhibited large solubilities in hot aqueous solutions of NH 4OH.