Electric Field Induced Intermediate Phase Near the Ferroelectric Lock-In Transition in Rb₂ZnCl₄

In the presence of a strong external electric field, a diffuse intermediate phase is shown to exist in Rb2ZnCl4 between the incommensurate and the commensurate phases. High resolution γ-ray diffraction in combination with in situ dielectric experiments yields detailed information about this unusual sequence of phase transitions that is most probably due to the accumulation of charged defects. The kinetics of field-induced transitions is studied by stroboscopic diffraction on a millisecond time-scale demonstrating that also mechanical strains play an important role for the transition mechanism.