J. Slak

Proton NMR study of the structural phase transitions in perovskite layer compounds: (CnH2n+1NH3)2CdCl4 and (NH3–(CH2)n–NH3) CdCl4

The temperature dependences of the second moments M2 of the proton magnetic resonance absorption spectra and of the proton spin–lattice relaxation times T1 of perovskite layer compounds (CnH2n+1NH3)2CdCl4 with n=1–3 and (NH3– (CH2)n–NH3) CdCl4 with n=2−5 have been studied together with the frequency dispersion of T1. The structural phase transitions in these compounds were found to be connected with a change in the state of motion of the alkyl or alkylene groups, i.e., by an interplay of transitions between different N–H−−−Cl hydrogen bonding schemes and the excitation of hindered rotations of the hydrocarbon chains.

Proton NMR relaxation of adsorbed water in gelatin and collagen

The dependence of the water self-diffusion coefficients as well as of the proton spin-lattice and spin-spin relaxation rates on the concentration have been studied in the gelatin-water system and in hydrated native collagen. The bound and free water fractions and the corresponding spin-spin and spin-lattice relaxation rates have been determined within the multi-phase water proton exchange model. Various theoretical models for the water proton cross-relaxation to the biopolymer have been studied and the results compared with the observed Larmor frequency dependence of the water proton spin-lattice relaxation rate.

133Cs Spin‐Lattice Relaxation and Resonance in Ferroelectric CsD2AsO4 and CsH2AsO4

The electric field gradient (EFG) tensor at the Cs sites in CsH2AsO4 and the 133Cs spin‐lattice relaxation rate in CsD2AsO4 have been determined. The results show that the time averaged value of the EFG tensor at the Cs site in the paraelectric phase is the average of the two ferroelectric EFG tensors for opposite directions of polarization, and that the time dependence of the Cs EFG fluctuations is determined by the same dynamic process which governs the EFG fluctuations at the deuteron sites in the O–D ··· O bonds.

1D and 2D NMR study of ionic conductivity in CsDSO4

Abstract The 133 Cs and deuteron NMR measurements of the superionic transition in CsDSO 4 showed that the mechanism of protonic conductivity involves thermally-activated hopping of deuterons over well-defined lattice sites. The present 2D exchange NMR study of O–D...O deuteron interbond motion provided evidence that slow deuteron exchange between two differently oriented hydrogen bonds in the unit cell of CsDSO 4 already takes place at room temperature, thus indicating precursor effects of the superionic transition far below the transition temperature T 0 =412 K.

31P chemical shift and relaxation study of the pseudo‐one‐dimensional ferroelectric transition in CsD2PO4

The 31P chemical shift tensors σ have been determined above and below Tc. The spin–lattice relaxation time T1 (31P) was measured as a function of temperature at 109.3 and 36.4 MHz. The paraelectric 31P chemical shift tensor was found to be the average of the two tensors observed in the ferroelectric phase. This shows that the phase transition is triggered by the ordering of the O–H(2) ⋅⋅⋅O deuterons. The intrinsic O–H(2) ⋅⋅⋅O deuteron intrabond jump time is, in the absence of the interactions, of the same order as in KD2PO4. The anomalously short T1 (31P) is the result of an ’’anisotropy slowing down’’ of the order parameter fluctuations due to the pseudo‐one dimensional nature of correlations in CsD2PO4.

Deuteron magnetic resonance study of the antiferroelectric phase of ND4D2PO4

The O–D ⋯ O deuteron quadrupole coupling tensors have been determined in the antiferroelectric phase of ND4D2PO4. The results show that the antiferroelectric phase transition in ND4D2PO4 is connected with an order‐disorder transition of the deuterons in the O–D ⋯ O bonds and that the Nagamiya model of hydrogen ordering is correct.

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 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.

Deuterium spin–lattice relaxation in ferroelectric triglycine sulfate

The ND3 deuteron spin−lattice relaxation time has been studied near the ferroelectric phase transition in single crystal triglycine sulfate. The results confirm proton−discorder motion in the hydrogen bond between glycine II and glycine III ions but they cast doubt upon the hypothesis concerning critical flipping of the glycinium I ion. Evidence is presented indicating faster hindered rotation of the glycinium I ND3 group compared to that of such groups at the other glycine ions.

9Be NMR Study of the incommensurate phase in (ND4)2BeF4 and (NH4)2BeF4

Abstract The 9Be quadrupole coupling tensor of (NH4)2BeF4 has been determined in the high temperature paraelectric (P) phase and the temperature dependence of the 9Be NMR spectrum and spin-lattice relaxation rate was studied in the intermediate incommensurate (I) and the low temperature commensurate (C) phase. A significant broadening of the satellites was found in the I phase which is of the same order as the splitting of the 9Be lines in the C phase. The results agree with a model where the I phase represents a sinusoidal ferroelectric modulation of the structure of the P phase, though higher harmonics cannot be excluded. Close to TI in the P phase and in the whole I phase the 9Be spin-lattice relaxation rate is determined by the incommensurate soft mode, but no anomalously large phason contribution was found.

On the dynamics of the pseudo one-dimensional ferroelectric ordering in CsH2PO4 and CsD2PO4

Abstract Measurements of the temperature dependence of the phosphorus Zeeman and dipolar spin-lattice relaxation times in CsH2PO4 show in the temperature range dominated by one-dimensional correlations an extremely strong dynamic central peak which decreases by four orders of magnitude on going to the range dominated by three dimensional correlations. The order fluctuation spectrum is qualitatively different in the case of CsD2PO4.