Nanocomposite based on semiconductor oxides SnO 2 /WO 3
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Nanocomposite based on semiconductor oxides SnO2/WO3 M.N.Rumyntseva, M.N.Boulova, D.A.Chareev, L.I.Ryabova, B.A.Akimov1, A.M.Gaskov Chemistry Faculty, Moscow State University, Moscow 119899, Russia 1 Low Temperature Physics Department, Moscow State University, Moscow 119899, Russia ABSTRACT Nanocrystalline SnO2 and WO3 and nanocomposite with Sn:W ratio 1:9, 1:1, 9:1 were prepared by co-precipitation of α-stannic and tungstic acids. Phase composition and average crystallite size were determined from XRD data. Presence of the second component results in the reduction of the crystallites growth rate, giving rise to the enhancement of thermal stability of nano-scaled system. TGA data allowed to estimate the concentration νH2O of water adsorbed on nanocomposite effective surface. Maximal νH2O value and the highest resistance were observed for nanocomposite with Sn:W = 1:1. The temperature dependence of resistance R reveals its activation character. The current-voltage curves are interpreted in terms of electrochemical capacitor recharge.
INTRODUCTION Metal oxides SnO2, ZnO, In2O3 in ultradispersed form are widely used as resistive type gas sensors. High values of gas sensitivity may be regarded as their main advantage, while microstructure stability being their main deficiency. The stability of the ultradispersed systems is heightened in more complicated materials containing an additional phase and characterized by non-homogeneous structure and composition: nanoheterogeneous materials or nanocomposites [1-3]. The reduction of the total area of the crystallite surface contacts for each of the ultradispersed phases slows down the growth of the grains. If the grain size of the oxides is comparable with the Debye length the introduction of new phases may also result in qualitative modification of material properties. Nanocomposites based on semiconductor metal oxides Me1O-Me2O with low mutual solubility are of a special interest as gas sensing materials. The present work deals with the synthesis, structure characterization and electric properties of SnO2 WO3 nanocomposites. The influence of the high temperature anneal together with the composition variation on the grain size in each phase is studied. The charge transport is found to involve ionic component, the conductivity activation energy is estimated. EXPERIMENTAL Nanocrystalline SnO2, WO3 and nanocomposite with Sn:W ratio 1:9, 1:1, 9:1 (samples Sn1W9, Sn1W1 and Sn9W1 respectively) were prepared by co-precipitation of α-stannic and tungstic acids. α-stannic acid was prepared by conventional hydrolysis of SnCl4 in ammonia water solution. Tungstic acid was obtained by hydrolysis of (NH4)10W12O41 in HCl water solution. Gels of the acids mentioned above were co-precipitated from the solution containing (NH4)10W12O41 and Na2[Sn(OH)6] prepared by reaction of α-stannic acid with 1 M NaOH. The V9.11.1
precipitates were centrifuged, washed with deionized water until the absence of chloride ion (AgNO3 test) and dried at 80° C for 24 h. Thermal anneals have been undertaken to st
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