Properties of trivalent-ion doped tungsten bronzes

Measurements of the electrical conductivity and the Hall coefficient have been made on polycrystalline yttrium-doped tungsten oxide, Y _x WO₃, for 0.05 ≤ x ≤ 0.20. This range of x includes the predicted metal–insulator transition. The results are compared with findings for La _x WO₃. Samples were prepared by solid-state reaction. Powder x-ray diffraction results for Y _x WO₃ show a single-phase perovskite cubic structure for 0.08 < x < 0.13, with additional phases occurring outside this range. Room temperature diffuse reflectance properties in the visible and infrared are dominated by the x-dependent metallic carrier concentration. The electrical conductivity and Hall effect results are similar to those of La _x WO₃ for x < 0.13, but show differences at higher x linked to the appearance of non-cubic crystallographic phases. The transport properties are typical of metal–insulator systems, with a change from metallic to activated behavior as x is reduced. The Hall results suggest that the trivalent ions donate their valence electron to the WO₃ conduction band.