INFLUENCE OF Tl+ DOPING ON OPTO-STRUCTURAL AND ELECTRICAL PROPERTIES OF CHEMICALLY GROWN TUNGSTEN HETEROPOLYOXOMETALATE THIN FILMS.

In present investigation, thin films of tungsten heteropolyoxometalates viz. undoped phosphotungstic acid [ H3 (PW12 O40)] and Tl+ doped phosphotungstic acid [Tl3 (PW12 O40)] were deposited at optimum deposition conditions by chemical growth process using organic and aqueous solutions of phosphotungustic acid and thallous acetate respectively. In this study, the optostructural and electrical properties of undoped and Tl+ doped tungsten heteropolyoxometalate thin films have been studied by scanning electron microscopy (SEM), atomic force microscopoy (AFM), X-ray diffraction, optical absorption, dc electrical resistivity and thermo-electric power techniques. Morphological study performed on scanning electron microscopy and atomic force microscopy shows after doping Tl+ there is formation of spherical shaped grains of Tl3 (PW12 O40) heteropolyoxometalate . X-ray diffraction study revealed that, the material is polycrystalline in nature having simple cubic spinel structure. After doping Tl+, intensity of prominent peak (311) increases and other peaks are suppressed, indicating intercalation of Tl+ in the octahedral lattice of phosphotungstate anion without change in crystal structure. The optical absorption study revealed that, there is decrease in band gap (Eg) of material after doping Tl+. DC electrical resistivity measurement study shows, after doping Tl+ the heteropolyoxometalate material Tl3 (PW12 O40) shows semiconducting behavior at lower temperature. The TEP study shows, generated voltage possesses plus sign over the whole range of temperature providing p-type semiconducting behavior. The TGA-DTA study revealed that, after doping Tl+, stability of Tl3 (PW12 O40) material increases and the material is thermally stable up to 265.12 °C. [ABSTRACT FROM AUTHOR]