Dielectric Properties of Nanocrystalline Tungsten Oxide in the Temperature Range of 223-293 K

The dielectric properties of nanocrystalline tungsten oxide are studied in the temperature range of 223-293 K and in the frequency range nu = 10(-2)-10(6) Hz. Powders of WO3 with particle sizes of 110, 150, and 200 nm are prepared by the heat treatment of ammonium paratungstate at various temperatures. It is established that the frequency dependences of the conductivity for all samples increase with an increase in frequency, while the polarization characteristics epsilon'(nu) and epsilon"(nu) decrease. It is found that the frequency dependences of the conductivity are described by a function of the form nu (s) with an index in the range of (0.83-0.90) +/- 0.01, which is characteristic of the "hopping" mechanism of charged-particle motion (complexes) over localized states confined by potential barriers and structural defects.