9Be Quadrupole Perturbed NMR Study of the Ferroelectric Transition in Deuterated Triglycine Fluoberyllate

The quadrupole perturbed magnetic resonance spectra of ⁹Be in a deuterated triglycine fluoberyllate single crystal have been studied as a function of temperature and crystal orientation, and the electric field gradient (EFG) tensors at the Be sites have been determined in the para‐ and in the ferroelectric phase. The data show that the main effect of the ferroelectric transition is a shift of the Be ion away from the twofold b axis where it lies in the paraelectric phase and a rotation of the two minor principal axes of the ⁹Be EFG tensor for $\text{θ = ± 25°}$ away from the average, paraelectric direction. The results can be understood in terms of the dynamic order—disorder model, proposed by Hoshino, Okaya, and Pepinsky.