What is it about?
A new analysis of published conductivity spectra of calcium-potassium nitrate (CKN), in its molten and glassy states, has brought to light a surprising continuity in its high-frequency (HF) behaviour, leading to unexpected simplicity. In particular, the activation energy and volume for elementary ionic displacements turn out to remain constant from 300 K in the glass up to 500 K in the melt, their ratio being the same as for their corresponding, but temperature-dependent DC analogues. On the sub-picosecond time scale, molten CKN thus seems to behave just like an elastic solid. Quite remarkably, this results in the published value for the HF shear modulus of glassy CKN matching almost exactly the ratio of activation energy to activation volume in the melt even far above Tg.
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Why is it important?
This result is significant because the behaviour of molten CKN is paradigmatic of fragile liquids quite generally.
Perspectives
For me, these results and the arguments developed in this paper provide clear and unambiguous support for the validity of Funke's MIGRATION concept. From a practical standpoint, the arguments presented here are relevant not only to the above-mentioned fragile liquids including ionic liquids and polymer electrolytes, but they also apply also to glassy electrolytes which may be used in all-solid-state batteries. The key factors influencing ion mobility in all these systems are the activation volumes for ion transport and the high-frequency shear moduli.
Prof. Malcolm David Ingram
University of Aberdeen
Read the Original
This page is a summary of: Ion Transport in Glass-Forming Calcium Potassium Nitrate: From Complex Behaviours to Unexpected Simplicities, Diffusion Foundations, May 2019, Trans Tech Publications,
DOI: 10.4028/www.scientific.net/df.22.140.
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