Fermi-level mediated acceleration of flash sintering of oxide ceramics

Qin-Kun Li; Evgeni S. Penev; Boris I. Yakobson

paper

Fermi-level mediated acceleration of flash sintering of oxide ceramics

arXiv:2607.23383

Abstract

The atomistic understanding of flash sintering (FS) remains speculative, despite its efficiency and versatility in materials processing. Employing first-principles calculations we demonstrate how charge compensation of a range of defects in the prototypical Y-stabilized cubic ZrO $_{2}$ (YSZ) shifts Fermi level E $_{F}$ up during FS, thereby accelerating cation migration for fast mass transport. The charge transition of Zr vacancy, V $_{Z r}^{q}$ , reduces its bulk diffusion barrier in V $_{Z r}^{- 4}$ during flash by 2 eV, relative to V $_{Z r}^{0}$ before flash, which is triggered by the charge equilibrium of nonstoichiometric defects. The substituent defect Y $_{Z r}$ , released by annihilating O vacancy, V $_{O}$ , in Y $_{Z r}$ V $_{O}$ Y $_{Z r}$ defect complex, acts as electron acceptor and favors V $_{Z r}^{0}$ before flash whereas excess V $_{O}$ , as electron donor thermally generated at the FS onset, upshift E $_{F}$ and thus support V $_{Z r}^{- 4}$ . The proposed mechanism of Fermi-level mediated cation diffusion for YSZ is generalized to other flash-sintered ceramics and has considerable bearing on the general theory of FS techniques in oxide ceramics.