Origin and consequences of the compensation (Meyer-Neldel) law

We have recently demonstrated that the Meyer-Neldel (MN) rule (compensation law) may be understood as arising naturally when the activation energy for a process is significantly larger than both the typical excitations available and kT. This conclusion was supported by the results of two microscopic models, related to special cases. In the present paper we present arguments, based on general results from statistical physics, which lead to the same conclusion. We show that this simple explanation also leads to the solution of a number of puzzles which have been associated with Meyer-Neldel behavior. We show that phenomena in groups of similar materials yield similar MN slopes. Finally, we show that the values of the slope for semiconductors with gaps in the 1–2-eV range are consistent with the suggestion that optical phonons are the source of the excitation energy in such processes.