Current-rate flash sintering of gadolinium doped ceria: Microstructure and Defect generation

In current-rate flash-sintering experiments the current is injected into the specimen from the very start and then increased at a constant rate, while the furnace is held at a constant temperature. The power supply remains under current control. The flash is induced at low current densities which reduces local heating at the electrodes. It leads to a uniform grain size across the entire gage length of the dog-bone specimen. This work pertains to 10 mol.% gadolinium-doped ceria flash sintered at current-rates ranging from 50 mA min(-1) to 1000 mA min(-1) at a furnace temperature of 680 degrees C. Full densities are obtained at a current density limit of 200 mA mm (2). Densification is shown to depend only on the instantaneous value of the current density, and not on the current-rate. The grain size, however, is shown to become finer at higher current-rates. A preliminary analysis of the energy deficit, that is, the estimated power input corresponding to the temperature as measured with a pyrometer, and the actual power consumption, estimates that huge concentrations of Frenkel defects may be introduced in the flash process. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.