Conduction paddle-wheel

The algorithms of Voronoi polyhedra construction may easily be used for the high-throughput analysis of new materials to identify the presence ofan infinite network of channels with suitable size for ionic conductivity or molecular diffusion. At the same time, the approach has a limited applicability for those systems where the topological and geometric factors do not play a significant role, such as proton conductors, or where the framework is not truly immobile and participates in the conduction process, for example, via a paddle-wheel mechanism. 

The above point is illustrated well by work on Li2S04 and LiNaS04. Two models existed to describe the ionic conduction in such materials and no consensus had been reached despite a vehement debate over almost 20 years. The paddle wheel model suggested that diffusive motion of Li+ (or Na+) must... 

The observations summarised here show that the high temperature polymorph shows fast Li conductivity and dynamic orientational disorder of the sulfate groups. The coexistence of these two highly unusual properties in a crystalline salt leads to the attractive interpretation that these phenomena are linked. Considerable effort has gone into the examination of a model for correlated motion in this structure and this has led to the description of ionic mobility in the a-Li2S04 structure proceeding via what has become known as the paddle-wheel mechanism. This mechanism describes the sulfate as acting as a rotor which provides a... 

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