A solvothermal route for the synthesis of ammonium tungsten bronze

A solvothermal route has been successfully used to prepare hexagonal (NH4)( 0.33)WO3 directly from yellow monoclinic WO3 powders in pyridine at 350 deg rees C. The as-prepared product was dark blue, which was characterized by t he X-ray powder diffraction (XRD) method, transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS). XRD shows that phase-pure hex agonal (NH4)(0.33)WO3 has been prepared. TEM images show that the particles are in the shape of columns. XPS measurement indicated that the chemical s tate on the surface of (NH4)(0.33)WO3 is similar to that of (NH4)(6)W7O24H2 O. (C) 1999 Elsevier Science B.V. All rights reserved.