Nanoparticle tungsten trioxide thick films based on commercial WO3 nanopowder and powder mixtures with different concentrations of metals (Ag, In and Bi) were prepared by screen-printing onto alumina substrates. The changes in phase composition, crystallite size and cell parameters induced in tungsten trioxide thick films by the inclusion of metal impurities were investigated by X-ray diffraction (XRD). Some of the samples were further analysed using a high temperature XRD method.