Abstract
Flash sintering, a special case of electric field-assisted sintering, results in accelerated densification at lower temperatures than conventional sintering methods. However, the mechanisms remain elusive despite the wide application potential. In-situ electron microscopy studies reveal shrinkage of ZnO green bodies due to both heating and heating/biasing but show no obvious effect of the current on the behavior. In contrast, thin epitaxial ZnO films deposited on an Al2O3 substrate undergo a clear flash event during in-situ voltage application in the TEM, providing the first observation of flash sintering of a thin film. The specimen was captured in the high conductivity state where grain boundary motion was observed. The microscopic origins of the high conductivity state could not be detected, but may have the same underlying physical origin as the high conductivity memristive state.
Highlights
A wide range of studies have shown a dramatic effect of applied electric field or current on the sintering behavior of oxide ceramic powders
The main characteristic of flash sintering (FS) is the flash event, which is characterized by a runaway electrical resistivity drop [1,2], rapid densification [1] and photoemission [3,4] once a sufficiently high electrical field and temperature are reached in the sample
We focus on ceramic ZnO, an abundant, safe, inexpensive and relatively easy to process model material for many different kinds of applications such as thermoelectrics, electronics, optoelectronics and laser technology [34,35]
Summary
A wide range of studies have shown a dramatic effect of applied electric field or current on the sintering behavior of oxide ceramic powders. A special case of this electric field-assisted sintering is so-called flash sintering (FS). It was first reported in 2010 by Cologna et al [1], who showed that an external electrical field caused the sintering process to happen within seconds and at much lower temperatures than in the absence of a field. The main characteristic of FS is the flash event, which is characterized by a runaway electrical resistivity drop [1,2], rapid densification [1] and photoemission [3,4] once a sufficiently high electrical field and temperature are reached in the sample. The flash phenomenon has been observed in many different inorganic compounds. A few recent examples include: Al2 O3 [5,6]; TiO2 [7]; BaTiO3 [8,9]; doped CeO2 [10,11,12,13]; ZrO2 : 3 mol% and 8 mol%
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