The impact of structural changes in ZrO2-Y2O3 solid solution crystals grown by directional crystallization of the melt on their transport characteristics

This work shows the correlation between the crystal structure, phase composition and transport characteristics of ZrO2 based solid electrolytes depending on the concentration of the stabilizing impurity Y2O3. The crystals ZrO2 stabilized with yttrium oxide in a wide range of compositions (from 2 to 15 mol% Y2O3) were studied. The phase composition, twin structure, and conductivity of the crystals we determined for all concentrations by X-ray diffraction, transmission electron microscopy, Raman and impedance spectroscopy. The ionic conductivity of the crystals was changed nonmonotonic, with increasing Y2O3 concentration. The existence of two maxima of ionic conductivity at temperatures 800–900 °C for compositions ZrO2-3.2 mol% Y2O3 and ZrO2-8 mol% Y2O3 was established. We show that twin boundaries do not trigger any additional ionic conductivity acceleration mechanism in ZrO2-Y2O3 crystals. The highest conductivity is observed in ZrO2-(8–10) mol% Y2O3 crystals containing the t″ phase in which the oxygen atoms are shifted from the high symmetry positions that are typical for the cubic phase.