page_title: Fast ion conductor
section_title: Superionic conductors
hierarchical_section_title: Fast ion conductor / Classification / Superionic conductors
caption_attribution_description: English: Despotuli,
context_page_description: In materials science, fast ion conductors are solids with highly mobile ions. These materials are important in the area of solid-state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. As solid electrolytes they allow the movement of ions without the need for a liquid or soft membrane separating the electrodes. The phenomenon relies on the hopping of ions through an otherwise rigid crystal structure.
context_section_description: Superionic conductors where Ωᵢ is more than 0.1 Ohm⁻¹ cm⁻¹ (300 K) and the activation energy for ion transport Eᵢ is small (about 0.1 eV), are called advanced superionic conductors. The most famous example of advanced superionic conductor-solid electrolyte is RbAg₄I₅ where Ωᵢ > 0.25 Ohm⁻¹ cm⁻¹ and Ωₑ ~10⁻⁹ Ohm⁻¹ cm⁻¹ at 300 K. The Hall (drift) ionic mobility in RbAg₄I₅ is about 2×10⁻⁴ cm²/(V•s) at room temperatures. The Ωₑ – Ωᵢ systematic diagram distinguishing the different types of solid-state ionic conductors is given in the figure.
  No clear examples have been described as yet, of fast ion conductors in the hypothetical advanced superionic conductors class (areas 7 and 8 in the classification plot). However, in crystal structure of several superionic conductors, e.g. in the minerals of the pearceite-polybasite group, the large structural fragments with activation energy of ion transport Ei  < kBT (300 К) had been discovered in 2006.
caption: Classification of solid-state ionic conductors by the lg (electronic conductivity, Ωe) – lg (ionic conductivity, Ωi) diagram. Regions 2, 4, 6 and 8 are solid electrolytes (SEs), materials with Ωi >> Ωe; regions 1, 3, 5 and 7 are mixed ion-electron conductors (MIECs). 3 and 4 are superionic conductors (SICs), i.e. materials with Ωi > 0.001 Ohm−1cm−1. 5 and 6 are advanced superionic conductors (AdSICs), where Ωi > 10−1 Ohm−1cm−1 (300 K), energy activation Ei about 0.1 eV. 7 and 8 are hypothetical AdSIC with Ei ≈ kBT ≈0.03 eV (300 К).
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