PROTONIC CONDUCTIVITY IN CA-DOPED YTTRIA

The ac conductivity of Ca-doped Y2O3 bas been measured as a function of doping level (0.3-10 mol% CaO), temperature (800-1200-degrees-C), partial pressure of oxygen (1-10(-20) atm) and of water vapour (3 x 10(-5)-2 x 10(-2) atm). The ac conductivity has been delineated into contributions from protons, native ions, and electron holes. The results can be rationalized in terms of a defect structure comprising electron holes, oxygen vacancies, and protons as the positive defects compensating the negatively charged dopant ions. The conductivities of protons, native ions, and electron holes all increase with the doping level up to about 1 mol% CaO. Above this dopant concentration the conductivity levels off, and this probably reflects that the solubility limit of CaO in yttria is then exceeded in this temperature region.