Beyond flash sintering in 3 mol % yttria stabilized zirconia

A flash sintering experiment can be carried out by applying an electric field and heating the specimen at a constant rate. The flash event occurs at a specific temperature that depends on the strength of the electric field. Alternatively, the furnace can be held at a constant temperature and the voltage applied as a step function; after an incubation time there is a highly non-linear rise in conductivity. This incubation step is called Stage I. The non-linearity is constrained by switching the power supply to current control. This short transient, during which the sample sinters nearly instantaneously, is the second stage. Under current-control, the (essentially dense) sample remains in a highly excited state indefinitely, which we call Stage III. In this state, the samples are often brightly electroluminescent emitting a green glow; unusual phase transformations occur and the rate of chemical reactions is greatly enhanced. We infer that these manifestations are evidence of a defect catastrophe that includes unusual generation of electrons, holes and point defects, which can produce sintering, electronic conductivity, electroluminescence, and phase transformations, all at the same time. We hypothesize that both Joule heating and electric field are necessary for this catastrophe.