Electrically switchable vacancy state revealed by in-operando positron experiments

TL;DR

This study uses in-operando positron experiments to reveal that electrical current can reversibly induce vacancy formation in copper, demonstrating a non-equilibrium defect process contributing to the flash state.

Contribution

It provides direct experimental evidence of electrically switchable vacancy states and non-equilibrium defect production in a metal, advancing understanding of flash phenomena.

Findings

Vacancy population increases above baseline with applied current and is reversible.

Current-induced vacancy concentration exceeds thermal equilibrium by over a million times.

Vacancy formation is only present during current application and vanishes within minutes.

Abstract

Whether the flash state in electrically driven solids involves non-equilibrium defect production or is accounted for by Joule heating alone has been debated since 2010. Using positron annihilation spectroscopy on copper, we observe a fully reversible, electrically switchable vacancy population: the DBS S-parameter rises above baseline whenever applied current exceeds a critical density and returns on current removal. Positron lifetime spectroscopy independently confirms open-volume defect formation and reveals a void to cluster relaxation hierarchy. The current-induced vacancy concentration exceeds the thermal-equilibrium value at 352C by > 106x, is present only while current is applied, and vanishes within minutes. The nucleation rate scales steeply with the applied current, connecting the minute-scale kinetics resolved here to the sub-second flash events observed in ceramic sintering. These results demonstrate current-induced Frenkel-pair production in a metal and identify a defect-mediated, non-equilibrium contribution to the flash state.