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

Abstract

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 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.

Stimulated-Echo NMR Spectroscopy of 9Be and 7Li in Solids: Method and Application to Ion Conductors

“…The temperature dependence of the resonance positions, presented in Fig. 1 for our protonated specimen, is compatible with 9 Be results published for a deuterated crystal [33]. Our measurements nicely document the line splitting occurring for T 5T C : Then spin-alignment spectra were recorded.…”

“…From the cited NMR investigations it was concluded that the rotation rate of the fluoberyllate tetrahedra is in the fast-motion regime much above the phase transition temperature ðT ¼ T C Þ and that it is in the slow-motion regime for T 5T C : The Be atoms were reported to shift concomitantly with respect to their high-temperature positions and the proton transfer within the N-H Á Á Á F bonds connecting the glycines with the BeF 2À 4 groups ceases at low temperatures. However, no information seems to be available regarding the time scale of motions which modulate the EFG tensor at the Be site [19,33].…”

“…The dipolar probes 1 H and 19 F were used to determine spin-lattice relaxation times [19]. In its deuterated form angle-dependent measurements of 9 Be spectra yielded quadrupolar coupling constants e 2 qQ=h of about 130 kHz [33]. As a function of temperature the asymmetry parameter Z Q was found to vary from 0.43 to 0.64.…”

EPR of the Four‐Copper‐Ion Complex with Spin S = 2 in Triglycine Fluoroberylate Monocrystal

“…As shown by Blinc et al [7], TGFB close to the Curie point reveals a marked anomaly of the electric field gradient causing, in our case, a change in zero splitting of the spin energy-levels [l].…”