Formation of defect-enriched phases far from equilibrium as a flash sintering mechanism
March 10-15, 2019
Flash sintering is a non-equilibrium phenomenon that manifests itself in rapid densification of green bodies, non-linear rise in the electrical conductivity and light emitted by electroluminescence. The underlying physics of this combination of phenomena remains puzzling. Flash sintering experiments in poly- and single-crystal ceramics imply the formation of phases far from equilibrium. These phases are considered to be enriched by Frenkel defects which separate into charge neutral vacancies and interstitials as well as electron‐hole pairs, explaining the unique observations of flash sintering. We hypothesize that these crystal defects are being generated due to a fast proliferation of short-wavelength lattice vibrations. This hypothesis is supported by recent experiments, where the Debye-temperature was found to be a lower bound for the onset of the flash.
In this talk, we will show by means of Molecular Dynamics simulations of single crystal aluminum, that a non-equilibrium state enriched by Frenkel pairs can be induced by excitation of short-wavelength lattice vibrations with a high rate. We find that Frenkel interstitials are only created above the Debye temperature, but much below the melting point. The molar concentration of the Frenkel pairs is far above equilibrium. While these results were found for Al, we discuss the universality of this mechanism on the example of rutile TiO2. First simulation results indicate, that Frenkel pairs are also generated in TiO2, where oxygen atoms take interstitial lattice sites.
Malte Jongmanns and Dietrich E. Wolf, "Formation of defect-enriched phases far from equilibrium as a flash sintering mechanism" in "Electric Field Enhanced Processing of Advanced Materials II: Complexities and Opportunities", Rishi Raj, University of Colorado, USA Olivier Guillon, Forschungzentrum Jülich, Germany Hidehiro Yoshida, National Institute for Materials Science, Japan Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/efe_advancedmaterials_ii/80