VIBRONIC THEORY OF THE STABILITY AND HYSTERESIS IN BISTABLE MIXED-VALENCE MOLECULAR SALTS

We previously proposed a two-orbital cooperative adaptation of the vib ronic Piepho-Krausz-Schatz model, for modeling the solid-state propert ies of biferrocenium mixed-valence salts. The resulting molecular ferr o-electric model, treated in mean-field approach, leads to remarkable double-reetrance at low temperature, following the sequence ferro-para -ferro-para-electric with increasing temperatures. Here we investigate some aspects of the phase diagram of the system: we unambiguously ass ess the metastable character of the second-reentrant state and we stud y the hysteresis loops associated with the first-order transitions whi ch result from orbital crossovers in the model.