Thermodynamics of solid electrolyte interfaces

So far the description has been focused on interfaces between liquid metals and electrolytes. These systems served preferentially for fundamental experiments because of the easy access to the free surface energy by just measuring surface tension. The situation becomes more complicated if a solid electrode is considered. For a solid electrode one must distinguish the work connected with the creation of a new interface, e.g., by cleavage from the work required to increase the surface area by stretching. 

In the first case the atom density in the surface remains constant at least as long as no restructuring occurs. The transfer of atoms from the bulk into the newly created surface increases the surface area. As the process is the same as for liquid electrodes, this may be termed surface energy a. In the review of Linford this contribution is called superficial work.  

The second contribution to the surface energy is new because it is based on an extension of the atomic distances in the surface area by a force called surface stress. The symbol used for the surface stress in this book is T as in the review of Linford. The surface stress is a tensor with the tensor components T, T, T, and T. The tensor is only independent in its direction for an isotropic sohd. The surface stress causes an elastic deformation of the surface described by the surface strain tensor e.  

Otherwise, a deformation can have two components the above-mentioned elastic deformation g and a plastic deformation by replacing atoms from the bulk into the surface Sp. Both parts of the surface strain were combined to a new function derived by Everett and Couchman. i 

A good name for this function is surface tension. In the review of Linford this contribution is called surface energy.  

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