Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 45: ZnO II

HL 45.2: Talk

Thursday, March 29, 2007, 14:15–14:30, H17

Electrical properties of compacted zinc oxide nanoparticles — •Sonja Hartner¹, Hartmut Wiggers², and Axel Lorke¹ — ¹Experimental Physics, University of Duisburg-Essen, Lotharstr.1, 47057 Duisburg — ²Institute of Combustion and Gas Dynamics, University of Duisburg-Essen, Lotharstr.1, 47057 Duisburg

The present study investigates the electrical properties of mechanically compacted pellets of nanosized zinc oxide powders from gas phase synthesis by impedance spectroscopy (IS). The measurements were performed in air and in hydrogen atmosphere at temperatures ranging from 320K to 650K. As expected for semiconducting materials, the spectra measured in air show very poor conductivity under ambient conditions and an increase in conductivity with increasing temperature. Between 500 K and 650 K the activation energy was found to be 604 meV. The impedance spectra exhibit the typical structure known from ionic conductors with a low-frequency Warburg impedance. After annealing at temperatures of about 250 °C in hydrogen atmosphere, the absolute value of the conductivity increases up to four orders of magnitude. The electrical measurements show ohmic behavior over the complete temperature range and the activation energy has changed to -11 meV, meaning positive temperature coefficient conductivity as it is known from metals. The change in electrical behavior under air and hydrogen is reversible and is attributed to a change of the chemical composition. The current understanding is that by exposing zinc oxide to hydrogen gas, oxygen vacancies are formed, providing ZnO1-x with free electrons which contribute to the overall conductivity.