Studies on the V₂O₅-TiO₂ system part 1. Thermoelectric power and electrical conductivity

Summary

The thermoelectric power and the resistivity of V₂O₅- TiO₂ mixtures over ranges of composition and temperature from 20° to 500° in air have been measured, The mixtures were obtained by coprecipitation of aqueous solutions of NH₄VO₃ and TiCl₄. calcined during 90 h at 550° and then sintered. Resistances were measured by the four points method.

At the VO_5/2 35–100% M range, the activation energies for conductivity change from 0,36 to 0.62eV, while for the thermoelectric power they change from 0,18 to 0.24eV. It can be assumed from these values that the conduction mechanism over this concentration range is due to the “hopping” of small polarons, arising principally, from the presence of V⁴⁺ ions.

In the samples with a high TiO₂ content, the activation energies for conductivity were 0.82 and 0.36eV, for the different samples.

From the variation of thermoelectric power with temperature, it can be assumed that the ionization energy of the donors centers lies at 0.83eV under the conducting band. A mechanism for band conduction is inferred from the results, being the V⁴⁺ donating centers and the V⁵⁺ receptive centers.