Densification of Y 2O 3 by Flash Sintering Under an AC Electric Field

In the present study, frequency dependence of the densification behavior of undoped Y₂O₃ sintered by the AC-flash sintering was systematically investigated at 500 V·cm⁻¹ over a frequency range from 0.05 Hz to 1 kHz. Flash events occurred at all frequencies when the power dissipation reached 10–20 mW·mm⁻³. The onset temperature for AC-flash sintering was in the range of 1230 °C–1300 °C. The Y₂O₃ bodies sintered under an AC field showed a uniform microstructure, without an asymmetric grain size distribution between the electrodes. The onset temperature for the flash sintering, final density, and grain size of the flash sintered specimens depended on the frequency. In particular, the Y₂O₃ body consolidated at 1 kHz exhibited a relative density greater than 99% and an average grain size of 1.6 μm. This almost full densification probably resulted from the high input power at the relatively high onset temperature of the AC-flash sintering at this frequency. The temperature dependence of the power dissipation during the AC-flash sintering experiments was influenced by the frequency of the applied field. The apparent dependence on the frequency can be ascribed to the periodic fluctuations of the specimen temperature at low frequencies and to the phase shift between the applied field and the specimen current at high frequencies.