Ferroelectric Phase Transition in Ammonium Hydrogen Bis (Chloroacetate). III. Chlorine-35 Quadrupole Relaxation

Abstract

The 35 Cl nuclear quadrupole resonance frequencies and relaxation times in ammonium hydrogen bis (chloroacetate) were measured in the ferro- and the paraelectric phases. The splitting of the resonance line in the ferroelectric phase shows the temperature dependence in the form of Δ ν=( T c - T ) 1/3 near the transition point T c . Sharp decrease of T 1 has been observed in the critical region and it was attributed to the critical slowing down of the electric dipolar interactions. Two kinds of relaxation mechanisms were examined: The order-disorder type of mechanism can explain the T 1 data of the paraelectric phase but it fails to explain the different temperature dependence of T 1 of ν 1 and ν 2 in the ferroelectric phase. The other mechanism, the displacive-mode transition is plausible because it gives a reasonable description of the T 1 anomaly both in the ferro- and paraelectric phases. This mechanism is also consistent with the structural evidences.