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Migration of Ag in low-temperature Ag2S from first principles
Zhongchang Wang1, Tingkun Gu, Takuya Kadohira
1Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. wang@cello.t.u-tokyo.ac.jp
The Journal of Chemical Physics
|January 15, 2008
Summary
Silver ion diffusion in silver sulfide (Ag2S) is primarily between different sites, not equivalent ones. This finding, supported by simulations, clarifies Ag ion mobility in low-temperature Ag2S.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Computational Physics
Background:
- Understanding ion diffusion in solid electrolytes is crucial for electrochemical devices.
- Silver sulfide (Ag2S) exhibits interesting ionic conductivity properties.
Purpose of the Study:
- To elucidate the migration pathways and activation energy barriers for silver (Ag) ion diffusion in low-temperature Ag2S.
- To determine the preferred diffusion mechanisms of Ag ions within the Ag2S lattice.
Main Methods:
- Density-functional theory (DFT) calculations.
- Nudged elastic band (NEB) method for pathway and barrier calculations.
- Ab initio molecular dynamics (AIMD) simulations for direct observation of diffusion.
Main Results:
- Calculated activation energy barriers for Ag+ diffusion between tetrahedral (T) and octahedral (O) sites and their vacancies (VT, VO).
- Identified that diffusion between nonequivalent sites (e.g., T to VO, O to VT) is energetically favorable over direct diffusion between equivalent sites (T to VT, O to VO).
- AIMD simulations confirmed the preferential diffusion pathways between nonequivalent sites.
Conclusions:
- Ag ion diffusion in low-temperature Ag2S predominantly occurs through pathways involving nonequivalent sites.
- Direct diffusion between equivalent sites is less likely than indirect pathways involving site transitions.
- Computational findings align with experimental observations, providing a detailed atomistic understanding of Ag+ transport.
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