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A three-phase system consisting of alumina (Al2O3), magnesia (MgO) and 8 mol% yttria‐stabilized zirconia (8YSZ) was reactive flash sintered to produce MgAl2O4-8YSZ composites. We show that a critical volume fraction of the ionic conductor 8YSZ is required to promote the flash phenomenon, indicating a typical percolation behavior. The easy path for conduction could be reached with a smaller critical volume fraction when using agglomerated powders for producing the green bodies. Furthermore, microstructure and X-ray diffraction analyses demonstrate that both sintering and phase transformation largely depend on the mixing level of the precursors. Although the presence of agglomerates resulted in a decrease of the flash onset temperature, poor sintering and incomplete phase transformation were verified. This behavior is attributed to inhomogeneous heat distribution within those samples during the flash state, which could be explained by the electrical current percolation.

We investigate the reactive flash sintering of Mg0.2Ni0.2Co0.2Cu0.2Zn0.2O precursor powders prepared by a polymeric synthesis route. The flash experiments were performed at a constant heating rate of 10 °C min−1 with electric fields from 15 to 60 V cm−1. The single-phase rock-salt structure was obtained in just a few seconds at furnace temperatures as low as 500 °C, under an electric field of 60 V cm−1 and a current density of 150 mA mm−2. Success at processing an entropy-driven phase in a remarkably short time and low furnace temperature demonstrates the potential of reactive flash sintering for producing entropy-stabilized materials.

We report the transformation of an amorphous mixture of Li0.5La0.5TiO3 (LLTO) directly into a single phase dense polycrystal, all within a few seconds at about 800 °C by the flash method. The starting material is a chemically-prepared precursor powder that experiences concurrent crystallization and densification to cubic LLTO during the flash event, as shown by in-situ X-ray measurements. The experiments were conducted at a constant heating rate with fields from 80 to 120 V cm−1 and a current limit of 60 mA mm–2. The resulting polycrystal yielded a bulk conductivity of 0.5 mS cm–1.

Short sintering times and low furnace temperatures characterize the flash sintering process. The method can enable sintering of compounds of lithium since, in conventional sintering, which requires several hours at high furnace temperatures, it can become difficult to control the retention of lithium. Cubic Li6.25La3Zr2Al0.25O12 with a relative density of 96% was sintered in a few seconds in air at a furnace temperature of 850 °C. These specimens had an ionic conductivity of 0.5 mS cm−1 at room temperature, and an activation energy of 0.35 eV. Transgranular nature of the fracture surface suggests strong cohesion at grain boundaries.

Higher electric fields lower the temperature for the onset of flash. We explore the question “what can be the lowest temperature for initiating flash?”. Constant heating rate experiments at increasing electric fields reveal a surprising characteristic: the Debye temperature emerges as a the lower bound for the onset of flash. Data for flash temperature for three oxides are shown to exhibit this behavior in a universal plot.

We discuss the Arrhenius behavior of electrical conductivity σ during flash sintering of 3 mol% yttria stabilized zirconia (3YSZ). In situ x-ray diffraction is used to determine sample temperature. Sintering contribution to σ is excluded by investigating the flash event on a dense ceramic. We show that total conductivity follows an Arrhenius-like equation in both dense and green samples, even during Stage II of flash. The non-linearity often verified during flash sintering of 3YSZ is therefore related to the furnace temperature instead of the sample temperature when building the ln(σ) vs. 1/T plots. Furthermore, we verified a change in the activation energy for conduction prior to the ignition of the flash event and discussed the possible mechanisms. For instance, the decrease in activation energy from Stage I to II in the dense sample is attributed to a contribution from electronic carriers.