Effect of zirconia doping on the electrical behavior of yttria
- PDF / 305,647 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 240 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Effect of zirconia doping on the electrical behavior of yttria C. C. Wang, V. D. Patton,a) and S. A. Akbar Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210
M. A. Alim The Ohio Brass Company, Hubbell Inc., Wadsworth, Ohio 44281 (Received 12 June 1995; accepted 17 August 1995)
The ac electrical behavior of yttria doped with a zirconia concentration ranging from 0.15 to 20 mole % is investigated in the temperature range of 800 to 1300 ±C. The ac electrical data, obtained in the range from 5 Hz to 13 MHz, indicated two distinct relaxations when analyzed in the impedance plane. These relaxations are attributed to lumped grains and trapping within grain boundaries, including possible electrode/sample effects. The admittance plane analysis revealed a semicircular relaxation in the low-frequency region, indicating identical response to that of the low-frequency relaxation of the impedance plane. The incorporation of zirconia into yttria is found to lower the activation energy of conduction in the grains and enhance ionic contribution to the overall electrical conduction. The PO2 studies and transference number measurements near atmospheric region indicate that p-type conduction dominates for the lightly doped yttria. An ionic contribution to the conduction processes becomes significant in heavily doped samples at/near atmospheric PO2 .
I. INTRODUCTION 1
A previous study on the ac electrical behavior of undoped yttria showed correlation between microstructures and electrical properties. Such a correlation is essential for the optimization of processing conditions of polycrystalline yttria for high-temperature thermistor applications.2 In this work, the electrical behavior of zirconia-doped yttria (YZ) is reported. This paper emphasizes the ac electrical characteristics associated with the grains, grain boundaries, and other phases including electrode effects. These characteristics are determined via immittance (impedance or admittance) measurements using the lumped parameter/complex plane (LPyCPA) technique. This technique has proven to be a useful means of characterizing heterogeneous devices,3–11 especially for extracting the contributions from individual charge carriers and physical regions of significance within the polycrystalline materials to the total electrical behavior. The YZ system was chosen in this study because (i) a large range of solubility exists in the yttria-zirconia system (at 1500 ±C, for example, 20 mole % zirconia can be dissolved in yttria12 ), and (ii) oxygen interstitials created by the addition of zirconia to yttria13,14 may change the dominant p-type conduction of undoped yttria14–17 to ionic conduction, which in turn may yield more stable thermistor materials. It has been reported14,18–20 that the p-type conductivity commonly observed for undoped a)
Presently at General Electric Lighting, Cleveland, Ohio.
422
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 2, Feb 1996
Downloaded: 13 M
Data Loading...
