THE AC ELECTRICAL BEHAVIOR OF POLYCRYSTALLINE YTTRIA

The ac electrical behavior of the polycrystalline yttria was evaluated in the temperature range of 800-1300 degrees C in air as a function o f frequency (5 Hz less than or equal to f less than or equal to 13 MHz ). Resistance-temperature and resistance-time (aging) characteristics were examined using immittance measurements and electron microscopy to establish microstructure-property relationships. The ac electrical da ta indicated two distinct relaxations when analyzed in the impedance p lane. These relaxations are attributed to the lumped grain and grain-b oundary contributions in conjunction with a polarization effect at the electrode/sample interface. The admittance plane analysis revealed a semicircular relaxation in the low-frequency region, indicative of a t rapping effect associated with grain-boundaries and the electrode/samp le interface. The variation in the total electrical resistance with ti me is found to be dependent on the starting microstructure of the samp le. A sample with a larger grain size shows a smaller degree of aging at elevated temperatures. Immittance measurements suggest that the maj or contribution to the aging behavior comes from the evolution in the microstructure. (C) 1995 American Institute of Physics.