PROTONIC CONDUCTION DOMAIN OF INDIUM-DOPED CALCIUM ZIRCONATE

The conductivities of a protonic conductor, 10 mole percent (m/o) In2O 3-doped CaZrO3, were measured in an atmosphere containing hydrogen or deuterium with the 4-wires ac impedance technique at temperatures rang ing from 623 to 1673 K. In high oxygen activities, H+/D+-isotope effec ts were observed below about 1100 K. The ratio of conductivities of pr otons to deuterons increased as the temperature decreased and rose to about 1.6 at 673 K. It was made clear by this observation that at low temperatures electrical conduction is dominated by proton and at high temperatures by positive hole, respectively. On the other hand, at hig h hydrogen activities, the isotope effects were observed up to about 1 600 K and it was concluded that proton is dominant below this temperat ure. Over that temperature, the isotope effects vanished and the elect rical conductivities were independent of gas potentials. It was conclu ded that electrical conduction over 1600 K was dominated by oxide ions . As electrical carriers obey the thermally activated process, the act ivation energies were calculated by the least squares method. The obta ined activation energies of protons, deuterons, positive holes, and ox ide ion vacancies were 0.74 +/- 0.05, 0.70 +/- 0.05, 1.21 +/- 0.07, an d 2.5 +/- 0.5 eV, respectively. Based on the model of defects equilibr ia and these experimental findings, the protonic conduction domain of the specimen was determined and is represented in temperature-potentia l diagrams.