Ionic and electronic transport in the fast Ag+ conductor α*-Ag3SI

M. Gombotz*, I. Hanghofer, S. Eisbacher-Lubensky, H. M.R. Wilkening

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Understanding the manifold origins that lead to fast ion transport in crystalline and amorphous solids is a vital topic in materials science. To advance in this field, the study of ion dynamics in model substances, partly inspired by applications, is a suitable route to identify the most important cause of ultrafast ion exchange processes in selected classes of materials. The ternary compound Ag3SI, which crystallizes with different space groups, represents such a model substance; its complex Ag-sublattice offers many, only partly occupied and adjoining Ag+ sites that guarantee a very high Ag+ ion conductivity. Here, we used broadband impedance spectroscopy and studied the temperature stability of the ionic conductivity of the α* phase of Ag3SI at a given temperature. β-Ag3SI, synthesized by a mechanochemical approach combined with a subsequent annealing step, transforms into the α form at high temperatures. Quenching this phase leads to (metastable) α*-Ag3SI that is characterized, at 20 °C, by a conductivity σ of 38 mS cm−1. The corresponding activation energy turned out to be 200 meV. Storing α*-Ag3SI at 30 °C for 140 h causes σ to drop to ca. 15 mS cm−1 (30 °C). A more drastic decrease is seen for the sample when annealed in situ at 60 °C resulting in 9 mS cm−1 (60 °C). For comparison, the thermodynamically stable β form is characterized by 3 mS cm−1 (20 °C). This high Ag+ ion dynamics is confirmed by 109Ag NMR which yields a single, sharp line at room temperature. Importantly, we also measured electronic conductivities σeon to corroborate that σ is predominantly governed by ionic contributions. As an example, for the α* form room-temperature potentiostatic polarisation measurements yield σeon = 2.7 × 10−8 S cm−1, which is by a factor of 106 lower than its total conductivity of 38 mS cm−1. For β-Ag3SI the maximum electronic conductivity turned out to be ≈ 2.0 × 10−7 S cm−1.

Original languageEnglish
Article number106680
JournalSolid State Sciences
Volume118
DOIs
Publication statusPublished - Aug 2021

Keywords

  • Conductivity
  • Electronic conductivity
  • Metastable AgSI
  • Phase transition
  • Thermal stability

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cooperations

  • NAWI Graz

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