Nuclear Spin-Lattice Relaxation in Some Ferroelectric Ammonium Salts

M and 1H NMR, ionic motions and phase transitions in proton conducting MHSO4 (M = K, Rb, Cs, and NH4) single crystals

“…Miller et al [30] reported data for the 1 H spinlattice relaxation time, and based on their results, a new phase transition was proposed at 173 K to replace the one previously reported at 160 K; they observed a striking change in the 1 H T 1 at 173 K. However, the T 1 -1 for the 1 H in the NH 4 HSO 4 crystals used here was well defined by the BPP theory, and the proton T 1 -1 showed no sudden changes near 173 K. For spin-lattice relaxation rates, the experimental value of T 1 -1 can be expressed in terms of an isotropic correlation time τ c for molecular motions by using the BPP theory. The correlation time for the proton as a function of the inverse temperature is shown in Fig.…”

Study of molecular motion by1H NMR relaxation in ferroelectric LiH3(SeO3)2, Li2SO4·H2O, and LiN2H5SO4single crystals

“…It is commonly held that a good deal of information regarding the structures and internal motions of solids can be obtained by using nuclear magnetic resonance (NMR) techniques. [2][3][4] A prominent feature of the solids studied in this manner is that the protons act as resonant nuclei and that variations of their relaxation times with temperature can be used to detect ionic motion. From relaxation time measurements, it has been found that at temperatures in the neighborhood of compounds' phase transition temperatures, both the slope and the actual value of the relaxation time plotted as a function of temperature undergo abrupt changes; 5 it was concluded that a change in molecular motion accompanied the phase change in each case.…”

Thermal, dielectric and barocaloric properties of NH4HSO4 crystallized from an aqueous solution and the melt

“…Thus, the absence of the Pc ↔ P1 phase transition in RbHSO 4 is most likely associated not with the chemical pressure decrease but with the absence of ammonium ion which plays a significant role in the mechanism of related structural distortions in NH 4 HSO 4 [8,9].…”

“…Successive phase transitions in NH 4 [1,10,11]. Structural distortion at T 2 is driven by the tilting of the tetrahedra NH 4 + as well as the large changes in S -O stretching and bending vibrational modes [8,9]. Such a solely qualitative characterization of the mechanism of the symmetry change does not allow one to calculate simply the entropy change at the Pc ↔ P1 phase transition.…”

“…The most important peculiarities of NH 4 HSO 4 are associated, first, with the existence of spontaneous polarization in the restricted temperature range between T 1 = 270 K and T 2 = 154 K [1], second, with piezoelectric properties existed below T 1 and T 2 at least down to 77 K [1], third, with a possibility to be grown from the melt as well as an aqueous solution [2], fourth, with T-p phase diagram rich of pressure induced phases [3][4][5]. The crystal structure and mechanism of structural distortions in ammonium hydrogen sulfate were repeatedly discussed using the results of X-ray, neutron, NMR and Raman scattering investigations [1,[5][6][7][8][9]. The main conclusions of these studies can be formulated as follows.…”