Ae Ran Lim

39K nuclear magnetic resonance in a KHSO4 single crystal

The 39K NMR in a KHSO4 single crystal grown by the slow evaporation method was investigated by employing a Bruker FT NMR spectrometer, and the 39K quadrupole coupling was determined from the angular dependences of the four 39K±1/2↔1/2 central NMR transitions. There are two sets of crystallographically inequivalent K+ ions: K(1) and K(2). From these angular dependences, all lead to different values for the quadrupole coupling constant and asymmetry parameter: e2qQ/h = 1.06±0.07 MHz, η = 0.58±0.05 for the K(1) ion, and e2qQ/h = 1.45±0.07 MHz, η = 0.85±0.05 for the K(2) ion. The EFG tensors of K(1) and K(2) are asymmetric and the orientations of the principal axes of the EFG tensors do not coincide for the K(1) and K(2) sites. The K(1) ions surrounded by nine oxygen atoms are high in symmetry, while K(2) ions surrounded by nine oxygen atoms show low symmetry.

Local structure of LiB3O5 single crystal from 7Li nuclear magnetic resonance

The local structure of LiB3O5 single crystal was investigated with 7Li (I=3/2) nuclear magnetic resonance measurements. We observed four different spectra, which could be divided into two groups corresponding to two kinds of lithium atoms, LiA and LiB, lying at crystallographically equivalent sites and magnetically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature and are e2qQ/h=143±1 kHz and η=0.6±0.1 for 7Li. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have the same principal values of the electric field gradient tensor, but different orientations, and originate from magnetically inequivalent sites. Also, the 7Li spin-lattice relaxation rate was measured, and the measured relaxation rate was found to be proportional to the temperature. The temperature-dependent single phonon process is considered to be more effective than the Raman ...

Molecular Motion Studied by Proton Magnetic Resonance in a [N(CH3)4]2ZnCl4 Single Crystal

The proton NMR line width and spin–lattice relaxation times for [N(CH3)4]2ZnCl4 single crystal were studied over a wide temperature range. Proton spin–lattice relaxation time measurements on [N(CH3)4]2ZnCl4 yielded a minimum, which were attributed to the effect of molecular tumbling. It seems obvious that the high-temperature minima of T1 is attributable to the tumbling motion of [N(CH3)4] ions, and that the T1 below 161 K is attributable to the same molecular motion which dominates at 210 K. Then, the T1 below 161 K undergoes a slow motion. The activation energies in phase VI and IV were determined to be 13.94 and 22.49 kJ/mol, respectively.

Ferroelastic Domain Switching Behaviour of [N(CH3)4]2CuCl4 and [N(CH3)4]2ZnCl4 Single Crystals Studied by External Stress

We studied the temperature dependence of the stress-strain hysteresis in [N(CH 3 ) 4 ] 2 CuCl 4 and [N(CH 3 ) 4 ] 2 ZnCl 4 single crystals grown by the slow evaporation method. From the obtained re...

The T1ρ 13C spin-lattice relaxation time of interpenetrating networks by solid state NMR

Abstract Poly (2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate) interpenetrated with 5% SiO 2 (PHEMA-IPN) were studied by 13 C CP/MAS NMR. From these results, the structure of two polymers were verified by 13 C NMR. Spin-lattice relaxation times for the polymer carbons in the rotating frame, T 1 ρ , have been measured as a function of temperature. The T 1 ρ spin-lattice relaxation times of the α -quarternary and carbonyl in the PHEMA and PHEMA-IPN undergo slow motions, i.e., motions on the slow side of the T 1 ρ minimum, while those of the 1-,2-, β -methylene, and 3-methyl undergo fast motions, i.e., motions on the fast side of the T 1 ρ minimum. From these T 1 ρ spin-lattice relaxation times, we discuss the mobility, the correlation time, and activation energy for the PHEMA and PHEMA-IPN, respectively. The activation energies for the PHEMA-IPN were found to be generally higher than those of PHEMA. The higher activation energy for the side-chain 2-methylene in the PHEMA-IPN is attributed to bonding between the SiO 2 and the hydroxyl group of the PHEMA.

Ferroelastic domain switching behaviour of single crystals

We investigated ferroelastic domain switching due to stress in single crystals grown by a slow evaporation method. The ferroelastic domain switching stress due to the saturation effect is about 0.9 MPa. The temperature dependence of the stress-strain hysteresis was also studied. From this result, it was determined that the single crystal undergoes a phase transition near K. In other words, the phase transition due to an external mechanical stress applied to crystals causes a transformation from the ferroelastic to the paraelastic phase. From these results, it was confirmed that crystals have ferroelastic characteristics below .

Temperature dependence of 7Li NMR in a LiKSO4 single crystal

Abstract The temperature dependence of the 7Li nuclear magnetic resonance in a LiKSO4 single crystal grown by the slow evaporation method was investigated by employing a Bruker FT NMR spectrometer. The 7Li NMR spectra demonstrates the occurrence of the first-order phase transition at 190 K which is connected with a lowering of the Li+ site symmetry and formation of three kinds of ferroelastic domains. Below and above 190 K, the quadrupole coupling constants and asymmetry parameters of Li in LiKSO4 decrease as the temperature increases. The temperature dependence of the quadrupole parameters in the temperature range of 130–400 K is explained by a single torsional frequency of the LiO ion by means of the simple Bayer theory.

H1 and L7i nuclear magnetic resonance study of the superionic crystals K4LiH3(SO4)4 and (NH4)4LiH3(SO4)4

We have investigated the temperature dependences of the line shape, spin-lattice relaxation time, T1, and spin-spin relaxation time, T2, of the H1 and L7i nuclei in K4LiH3(SO4)4 and (NH4)4LiH3(SO4)4 single crystals. We compared the nuclear magnetic resonance (NMR) results obtained for the two crystals. According to the NMR relaxation results, the influences of the H and Li atoms of K4LiH3(SO4)4 crystals on the superionic phase transition TS are not significant, whereas the influences of the H and Li atoms of (NH4)4LiH3(SO4)4 crystals on TS are significant. The increase in the relaxation time of the hydrogen-bond protons in (NH4)4LiH3(SO4)4 crystals above TS indicates that the breaking of O–H⋯O bonds and the formation of new H-bonds with HSO4− contribute significantly to their high temperature conductivity. The main contribution to this conductivity at high temperatures is the mobility of the hydrogen-bond protons.

Paramagnetic to antiferromagnetic transition in AMnCl3 (A=Rb and Cs) single crystals as observed by 87Rb and 133Cs spin-lattice relaxation

RbMnCl3 and CsMnCl3 order antiferromagnetically at Neel temperatures TN=94.6 K and TN=67 K, respectively. The 87Rb and 133Cs spin-lattice relaxation times in these crystals were measured in the temperature range of 270–60 K. The large change in the relaxation rate that is observed near TN indicates that the magnetic phase in these crystals undergoes a paramagnetic to antiferromagnetic transition. In both crystals, the temperature dependencies of the relaxation rates for T TN are in accordance with a single-phonon process.

Phase Transition Mechanism Studied by 1H and 87Rb Spin-Lattice Relaxation Time in a RbHSO4 Single Crystal

The 1 H and 87 Rb NMR spin-lattice relaxation times for a RbHSO 4 single crystal were measured in the temperature range of 300–170 K for study of the paraelectric (I) to ferroelectric (II) phase transition near T c =264 K. Proton spin-lattice relaxation time on the RbHSO 4 yielded a minimum, attributed to the effect of molecular motion. The activation energy for the reorientational motion in phase I was determined to be 16.54 kJ/mol, whereas, for the molecular motion in the phase II it was 25.53 kJ/mol. The change of the 87 Rb spin-lattice relaxation rate near 264 K corresponds to a phase transition in the crystal. The temperature dependences of the relaxation rate for 87 Rb in this crystal were in accordance with the single phonon process dominated by the phonon mechanism. The activation energies in phases I and II were obtained to be 2.66 kJ/mol and 17.25 kJ/mol, respectively. From 1 H and 87 Rb NMR investigations, the phase transition does play an important role by Rb nucleus, although the activation e...