IONIC AND ELECTRONIC CONDUCTIVITIES OF HOMOGENEOUS AND HETEROGENEOUS MATERIALS IN THE SYSTEM ZRO2-IN2O3

In the system ZrO2-In2O3, the In2O3-doped ZrO2 phases (cubic, tetragon al and t') exhibit high ionic conductivity and the ZrO2-doped In2O3 hi gh electronic conductivity. These phases are in thermodynamic equilibr ium at high temperatures. The ionic conductivity of ZrO2 depends on th e crystal symmetry having the same In2O3 concentration. At 1000 degree s C, the highest conductivities were obtained for cubic ZrO2 doped wit h 25 mol% InO1.5. At lower concentrations, the ionic conductivity of c ubic-ZrO2 decreases due to a first-order phase transformation to the t etragonal (t') form. Single-phase In2O3 doped with ZrO2 is an n-type e lectronic conductor with a conductivity of up to 7 X 10(4) S/m in air. Point defect models for electronic conduction in In2O3 doped with ZrO 2 are discussed. Two maxima in the electronic conductivity have been f ound: one in the two-phase region and one in the InO1.5 single phase r egion. In the heterogeneous two-phase material cubic-ZrO2 + InO1.5, th e electronic conductivity increases abruptly up to 10(4) S/m with incr easing InO1.5 concentration. This material is a three-dimensional comp osite of ion- and electron-conducting phases. The origin of the maximu m in electrical conductivity in the heterogeneous two-phase region is discussed.