Flash sintering in oxides: The Debye temperature is not the limit

Herein, we investigate the onset behavior of flash sintering, a rather novel material processing method. A thermal runaway driven by Joule heating has established itself as the likely explanation for the general onset behavior of flash sintering, however, multiple experimental observations appear to directly contradict this idea. One such observation is that the material specific Debye temperature appears to be the lowest temperature at which the onset of flash sintering is possible in oxides. In this work, we test this Debye limit of flash sintering on barium titanate (BaTiO 3 ), strontium titanate (SrTiO 3 ), cobalt ferrite (CoFe 2 O 4 ), copper oxide (CuO), and titanium trioxide (Ti 2 O 3 ) and ultimately refute it. Furthermore, we apply a basic modelling approach to investigate whether the onset behavior of flash sintering at high electric fields can be explained by Joule heating alone. We apply our findings to data from the original studies and propose an alternative interpretation to the previously inferred hard limit at the Debye temperature.