A research team led by Prof. ZHOU Yanguang at Hong Kong University of Science and Technology has discovered a mechanism for rapid ion transport in solid materials, challenging the classic diffusion model. The study, published in Physical Review Letters, identifies collective vibrational dynamics as the key driver.
Using machine-learning molecular dynamics simulations of superionic silver telluride (α-Ag₂Te), the team found that ion migration results from cooperative action of two types of vibrational modes: unstable modes initiate ionic displacement while stable modes maintain cation-anion separation. This synergy facilitates fast diffusion.
A New Strategy for Faster Ions
Based on this insight, the team proposed a defect-engineering strategy to enhance ion diffusion. Simulations showed that introducing 10% Te²⁻ vacancies increased the silver ion diffusion rate from 0.84×10⁻⁵ cm²/s to 1.54×10⁻⁵ cm²/s at 500 K due to increased unstable modes.
A More Universal Framework
The researchers also developed a new model predicting ion diffusion coefficients based on the ratio of unstable modes, offering a more universal framework than the traditional Arrhenius equation. This model can account for different defect concentrations and thermodynamic conditions.
"The findings bridge microscopic atomic dynamics and macroscopic ion transport," said Prof. Zhou. The research provides guidance for designing faster-charging solid-state batteries and more efficient thermoelectric materials by tuning vibrational spectra.