Conductivity of SnO2-In2O3 nanocrystalline composite films

Abstract

The conductivity of films consisting of a mixture of SnO2 and In2O3 nanocrystals at 200–500°C was studied. Based on the experimental data, it was assumed that in films containing less than 20 wt % In2O3, the current flows along SnO2 nanocrystals. A model of conductivity in these films is presented; it includes an electron transfer from In2O3 to SnO2, which forms positively charged In2O3 nanocrystals that contact the negatively charged SnO2 nanocrystals. In the presence of In2O3 nanocrystals, the activation energy of the electron transfer between SnO2 nanocrystals decreased substantially because of a decrease in the barrier of electron transfer between SnO2 crystals under the action of the negative charge. As a result, a percolation cluster of charged SnO2 crystals formed. At high contents of In2O3 (over 20 wt %), the conductivity increased dramatically. The curve of the temperature dependence of conductivity changed because of the appearance of a percolation cluster of In2O3 nanocrystals, in which the current passed. The conductivity of a mixed film of this kind differed from that of the nanocrystalline film of pure In2O3.