NMR Investigations of Molecular Motions and Critical Dynamics at the Ferroelectric Phase Transition of Tris‐Sarcosine Calcium Chloride

Abstract

Abstract35Cl and 81Br quadrupolar perturbed NMR measurements in single crystals of tris‐sarcosine calcium bromide (TSCB) and tris‐sarcosine calcium chloride (TSCC) are used to study molecular motions and the dynamical critical behaviour near the ferroelectric phase transition of TSCC. At temperatures higher than about 130 K the spin‐lattice relaxation time T1 of 81Br nuclei in TSCB is dominated by an activated process with an activation energy of 28 kJ/mol which is attributed to the reorientation of parts of the sarcosine molecule. The results are compared with those obtained from 35Cl measurements of TSCC. Near the ferroelectric phase transition of TSCC at 131.5 K a critical contribution to the 35Cl spin‐lattice relaxation rate is observed which can be explained on the basis of the standard mean‐field model in accordance with the static critical behaviour below Tc.