Order-disorder dynamics of the ferroelectric phase transition in tris-sarcosine calcium chloride crystals.

Abstract

Critical anomalies in the ${\mathrm{Mn}}^{2+}$ impurity spectra near the ferroelectric phase transition in tris-sarcosine calcium chloride (TSCC) crystals have been interpreted in terms of a collective fluctuation in the polar pseudospin system representing Ca(sarcosine${)}_{6}$ complexes in the lattice. The anomalous line broadening in the paraelectric phase was found to be closely related to the splitting of the line below the transition temperature ${T}_{c}$. At temperatures close to ${T}_{c}$ in the ferroelectric phase the line shape was asymmetrical, indicating that sinusoidally distributed pseudospins were randomly sampled by ${\mathrm{Mn}}^{2+}$ impurities. The time scale of EPR measurements modified the line shape, where the presence of a slow fluctuation between the pair of lines was evident. Contrary to recent spectroscopic and dielectric results on TSCC crystals, the critical anomalies in the ${\mathrm{Mn}}^{2+}$ spectra were well resolved to give grounds for the order-disorder dynamics of the transition.