Ionic mobilities and association energies from an analysis of electrical impedance of ZrO2-Y2O3 alloys

The de conductivities of ZrO2-Y2O3 ceramic alloys (in the range 3-12 mol% o f Y2O3) have been obtained from ac impedance measurements at temperatures b etween 250 degrees and 370 degrees C, The Almond-West ac conductivity model has been applied to evaluate hopping rates in this system, The migration e nthalpies mere evaluated and shown to increase with yttria concentration, b ut all values determined were shown to be lower than the corresponding acti vation enthalpies for conductivity. The association enthalpies thus calcula ted mere shown to be very small in 3 mol% Y2O3-ZrO3 and to increase with yt tria concentration until the yttria contents were high enough to form fully stabilized cubic zirconia, For these samples the association enthalpies ar e about 0.19 eV, and no longer sensitive to yttria content. The low hopping rate at high yttria concentration might be attributed to low entropy in th e system, which might be attributed to the formation of vacancy clusters an d/or an ordering of the structure.