Measurement and modelling of electrical resistivity by four-terminal method during flash sintering of 3YSZ

Flash sintering is a newly developed technique to quickly density conductive ceramics in the presence of an electric field. At a critical combination of field and temperature, densification takes place in a few seconds. This paper investigates the electrical resistivity during flash sintering of 3YSZ by the four-terminal method in combination with numerical modelling of electrical heating and temperature distributions. Densification rates were similar to those observed previously in specimens rapidly heated by methods not involving direct electrical heating. Temperature gradients caused by heat loss from the surface and non-uniform electrical heating led to differential sintering, specimen distortion and non-uniform grain size. The four point measurements revealed significant contact resistance at the power supply electrodes and allowed accurate measurement of the resistivity under the high current conditions of flash sintering. The specimen resistivity was lower for a given temperature under high current conditions and this was attributed to electronic conduction. Concurrent sintering led to a progressive reduction of resistivity during heating causing an increase in the apparent activation energy for electrical conduction. When the effect of sintering on resistivity was accounted for, the onset conditions for the flash event were accurately predicted on the basis of thermal runaway. (C) 2018 The Ceramic Society of Japan. All rights reserved.