PROTONIC CONDUCTION IN FE-DOPED KTAO3 CRYSTALS

The protonic conductivity of perovskite-structured KTaO3 crystals acceptor doped with Fe3+ is investigated as a function of P(O2), P(H2O) and dopant concentration. We show that Fe-doped KTaO3 is a protonic conductor after treatment in gases of low P(O2) ( < 10(-12) atm) and an electronic (hole) conductor after treatment in gases of higher P(O2). The protonic conductivity increases with increasing P(H2O), reaching a value of 5 X 10(-9) OEMGA cm-1 (at 500 K) after treatment in ps saturated with water vapor. The activation energy of protonic conduction ranges from 0. 73 to 1.02 eV for variously Fe-doped samples, increasing with increasing proton content, as monitored through the OH stretching vibrational band by infrared spectroscopy. In addition, Meyer-Neldel behavior is observed, i.e. the activation energy of conduction is proportional to the logarithm of the conductivity preexponential. The transport numbers for protons and oxygen ions are measured, indicating that the contribution to the conductivity from oxygen ions is minimal.