IMPEDANCE SPECTROSCOPY OF GRAIN-BOUNDARIES IN NANOPHASE ZNO

Sintered compacts of nanophase ZnO (similar to 60 nm average grain size, presintered at 600 degrees C) were made from powders (similar to 13 nm) prepared by the gas-condensation technique. Impedance spectra were taken as a function of temperature over the range 450-600 degrees C and as a function of oxygen partial pressure over the range 10(-3)-1 atm (550 and 600 degrees C only). The activation energy was determined to be 55 kJ/mole (0.57 eV) and was independent of oxygen partial pressure. The oxygen partial pressure exponent was -1/6. Impedance spectra exhibited nonlinear I-V behavior, with a threshold of approximately 6 V. These results indicate that grain boundaries are governing the electrical properties of the compact, Ramifications for oxygen sensing and for grain boundary defect characterization are discussed.