First‐principles prediction of fast migration channels of potassium ions in KAlSi₃O₈ hollandite: Implications for high conductivity anomalies in subduction zones

Abstract

Materials sharing the hollandite structure were widely reported as fast ionic conductors. However, the ionic conductivity of KAlSi3O8 hollandite (K‐hollandite), which can be formed during the subduction process, has not been investigated so far. Here first‐principles calculations are used to investigate the potassium ion (K+) transport properties in K‐hollandite. The calculated K+ migration barrier energy is 0.44 eV at a pressure of 10 GPa, an energy quite small to block the K+ migration in K‐hollandite channels. The calculated ionic conductivity of K‐hollandite is highly anisotropic and depends on its concentration of K+ vacancies. About 6% K+ vacancies in K‐hollandite can lead to a higher conductivity compared to the conductivity of hydrated wadsleyite and ringwoodite in the mantle. K+ vacancies being commonly found in many K‐hollandite samples with maximum vacancies over 30%, the formation of K‐hollandite during subduction of continental or alkali‐rich oceanic crust can contribute to the high conductivity anomalies observed in subduction zones.

The Electrical Conductivity of Liebermannite: Implications for Water Transport Into the Earth's Lower Mantle

“…Higher conductivity has also been observed in alkali bearing materials with the hollandite crystal structure (Khanna et al, 1981). Such higher conductivity is often referred to as superionic conductivity (He et al, 2016; Khanna et al, 1981). In our study, we are documenting such effects at extreme pressures of 12 to 24 GPa in libermannite.…”

“…More recently, the electrical conductivity of liebermannite, relevant for the deeply subducted crust, has been examined using molecular dynamics simulations. The predicted electrical conductivity for liebermannite with a 12.5% vacancy in the tunnel is ~20 S/m at 10 GPa and 1600 K (He et al, 2016). The magnitude of the predicted electrical conductivity resulting from ionic conduction of K + ions in the tunnels is significantly greater than that of the electrical conductivity due to extrinsic defects.…”

“…The unique crystal structure of liebermannite and the ability to accommodate large alkali ions and possibly H 2 O in its tunnels highlight its importance as a possible H 2 O repository in the subducted crustal components and a possible source for OIB. However, so far, studies on liebermannite have been restricted to the equation of state, elasticity (Caracas & Boffa Ballaran, 2010; Kawai & Tsuchiya, 2013; Mookherjee & Steinle‐Neumann, 2009), and electrical conductivity (He et al, 2016) of the dry variety.…”

A first-principles study on Si24 as an anode material for rechargeable batteries

“…Moreover, high-pressure induced phase transformations of several electrode materials, e.g., Li x MPO 4 (M ¼ Fe and Co), 8,9 16 In addition to these high-pressure polymorphs of current electrode materials, many novel alkali compounds with an open-channel structure have been derived at high pressure. 12,[17][18][19] It has been proven that these channels likely provide a diffusion path for the alkali ions and lead to high ionic conductivities. 12,18 Although these materials have potential application for batteries, related investigations are rare.…”

“…12,[17][18][19] It has been proven that these channels likely provide a diffusion path for the alkali ions and lead to high ionic conductivities. 12,18 Although these materials have potential application for batteries, related investigations are rare. Therefore, it is necessary to exploit their potential as electrode materials for LIBs and SIBs.…”