# Variation of ionic conductivity in a plastic-crystalline mixture

## TL;DR

This study explores how mixing different plastic crystals affects ionic conductivity, revealing that the coupling between ion movement and molecular reorientation remains consistent across compositions, unlike in succinonitrile mixtures.

## Contribution

It provides a detailed analysis of phase behavior and charge transport mechanisms in cyclohexanol and cyclooctanol mixtures with lithium ions, expanding understanding beyond succinonitrile-based systems.

## Key findings

- All mixtures exhibit plastic-crystalline phases with glass transitions.
- Conductivity is dominated by the 'revolving-door' mechanism.
- Coupling between ionic and molecular dynamics remains stable across compositions.

## Abstract

Ionically-conducting plastic crystals are possible candidates for solid-state electrolytes in energy-storage devices. Interestingly, the admixture of larger molecules to the most prominent molecular PC electrolyte, succinonitrile, was shown to drastically enhance its ionic conductivity. Therefore, binary mixtures seem to be a promising way to tune the conductivity of such solid-state electrolytes. However, to elucidate the general mechanisms of ionic charge transport in plastic crystals and the influence of mixing, a much broader data base is needed. In the present work, we investigate mixtures of two well-known plastic-crystalline systems, cyclohexanol and cyclooctanol, to which 1 mol% of Li ions were added. Applying differential scanning calorimetry and dielectric spectroscopy, we present a thorough investigation of the phase behavior and the ionic and dipolar dynamics of this system. All mixtures reveal plastic-crystalline phases with corresponding orientational glass-transitions. Moreover, their conductivity seems to be dominated by the "revolving-door" mechanism, implying a close coupling between the ionic translational and the molecular reorientational dynamics of the surrounding plastic-crystalline matrix. In contrast to succinonitrile-based mixtures, there is no strong variation of this coupling with the mixing ratio.

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Source: https://tomesphere.com/paper/1704.07802