Temperature dependence of the Mössbauer isomer shift

The isomer shift for nuclei in solids is calculated taking into account the core electron charge density, the overlap effects, the charge transfer effects, and the crystal field effects. The importance of the dynamical electron phonon interaction is pointed out. It is found that the phonon-induced dynamical configurational mixing and the dynamical charge transfer play an important role and contribute to a dynamical isomer shift which enhances the temperature-dependent second-order Doppler shift. It is found that the internal conversion and the electron capture give information which is related to the isomer shift. In mixedvalence compounds such as EuCu₂Si₂, the center shift of the M?ssbauer lines has been explained as if arising from the phonon-induced dynamical isomer shift.