Emergence and Extinction of a New Phase During On-Off Experiments Related to Flash Sintering of 3YSZ

The flash phenomenon occurs when oxide ceramics are heated above a threshold temperature under an applied electric field. It is defined as an abrupt increase in the conductivity of the specimen. The specimen then can be held in this state of high conductivity by switching the power supply from voltage to current control. Here, we report on the emergence of new X-ray diffraction peaks in 3 mol% yttria-stabilized zirconia (3YSZ) when the specimen is held in this current controlled state. These peaks are indexed as a pseudocubic phase of zirconia. The peaks extinguish and reappear when the field is turned off and on. The specimen temperature in the flash state is measured from the thermal expansion of platinum, which is placed as a thin film on a small portion of the specimen surface. Experiments without the electric field, at even higher temperatures than those measured with the platinum standard, do not show any change of phase, thus ruling out Joule heating as the cause of this phenomenon. The time dependency of the growth and dissolution of the pseudo cubic phase is reported. These in situ experiments were carried out at the Advanced Photon Source Synchrotron at the Argonne National Laboratory.