Insights into photoemission origins of flash sintering of ceramics

Electric field applied above a critical temperature leads to ultrafast densification of green ceramic compacts and simultaneous photoemission, termed flash sintering. A similar flash photoemission is also observed in single crystals with no need for sintering. Assuming the formation of a few atomic layer liquid-films at the particle/crystal surfaces due to local Joule heating or surface breakdown, one expects the exponential increase in the electric conductivity by current percolation through the liquid-film. At temperatures above the glass transition temperature of the otherwise crystalline film, high flux of excitons are formed by recombination of the injected electrons with electron holes. The corresponding momentum conservation for the indirect gap transition is assisted by the broad Boson peak of phonons at the low energy vibrational density of states (LEVDOS) of the amorphous/liquid-film. The glass transition temperature of the amorphous film sets the lower bound temperature for the flash event. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.