Theory of cross phenomena and their coefficients beyond Onsager theorem

IMPACT STATEMENT Through flux equations based on the combined law of thermodynamics, theory of cross phenomena is developed and applied to thermoelectricity, thermodiffusion, diffusion, electromigration, electrocaloric and electromechanical effects, and thermal expansion. Cross phenomena, representing responses of a system to external stimuli, are ubiquitous from quantum to macro scales. The Onsager theorem is often used to describe them, stating that the coefficient matrix of cross phenomena connecting the driving forces and the fluxes of internal processes is symmetric. Here we show that this matrix is intrinsically diagonal when the driving forces are chosen from the gradients of potentials that drive the fluxes of their respective conjugate molar quantities in the combined law of thermodynamics including the contributions from internal processes. Various cross phenomena are discussed in terms of the present theory.

Automated summary

Through the flux equations based on the combined law of thermodynamics, a theory of cross phenomena has been developed and applied to various fields. It is found that the coefficient matrix of cross phenomena exhibits a diagonal structure when the driving forces are chosen appropriately.