T. Apih

Dynamics of the superprotonic conductor K9H7(SO4)8·H2O studied by means of nuclear magnetic resonance

The dynamics of a recently discovered superprotonic conductor K9H7(SO4)8· H2O has been studied between 40 and 425xa0K by techniques based on the NMR spectrum shape, spin–lattice and spin–spin relaxation. At low temperatures (such as 40xa0K), proton intra-H-bond hopping is already intensive. At higher temperatures, water 180° reorientations become observable in the NMR experiments, whereas above 250xa0K, proton interbond jumps—a precursor of the superprotonic conductivity above the transition temperature Tsp = 398xa0K—become frequent. Above Tsp, a large increase in the proton spin–spin relaxation time T2 indicates that proton long-range diffusion becomes significant. Proton interbond jumps are assisted by reorientations of the SO4 tetrahedra, which also cause breaking of the water bonds, so water molecules become free and consequently diffuse out of the crystal. The loss of water allows rearrangement of the lattice, so the number of structurally equivalent proton sites in the superprotonic phase is increased, resulting in a very open structure for the hydrogen interbond transfer.

2D 39K NMR study of the phase transition in KSCN

Abstract Two-dimensional (2D) “separation of interactions” 39K 1 2 → −1 2 NMR measurements of KSCN show that the line broadening around and above Tc is purely homogeneous. The disordering process above Tc is thus of dynamic and not of static origin. The lifetimes of the orthorhombic microdomains which appear static on the neutron scattering time scale are between 10−3 and 10−7 s.

Microscopic model for the structural phase transitions in NH4SCN and KSCN

Abstract The 39K quadrupole coupling tensors and chemical-shift tensors have been determined in KSCN and the SCN and NH4 nitrogen quadrupole coupling tensors have been determined in NH4SCN as a function of temperature. The results for KSCN show, that the symmetry of the paraelectric phase is broken on the quadrupole-coupling time scale but not on the chemical-shift time scale, implying that the characteristic time for structural fluctuations is between 10−5 sec and 10−2 sec. The high temperature phase of NH4SCN is dynamically disordered with the hydrogen-bonded NH4 ions moving between 4 equivalent off-center sites. In the orthorhombic phase two of the 4 NH4-sites freeze out, so that this phase is partially ordered.

Precursors of Magnetic Resonance Imaging Contrast Agents Based on Cystine-coated Iron-oxide Nanoparticles

Super Paramagnetic Iron-Oxide Nanoparticles (SPION) are currently used as magnetic resonance imaging (MRI) contrast agents. The functionalization of their surface with organic and biocompatible molecules has the purpose to produce carriers selective for different tissues and organs. In this paper, we present the preparation of new cystine-coated ultra small super paramagnetic iron-oxide nanoparticles (USPION) of different core size, from 4 nm to 11 nm. The physical-chemical characterization of these nanoparticles was performed by using several experimental techniques, such as atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM) and magnetic measurements. 1 H NMR relaxation times at different magnetic field strengths have been measured for several water- dispersions of cystine-coated iron-oxide nanoparticles of the smallest dimensions (4 nm). These preliminary results confirm their potentialities as molecular imaging probes and MRI contrast agents.

Proton NMR study of molecular motion in bulk and in highly drawn fiber polyamide-6

The proton motion in bulk and highly drawn fiber polyamide-6 has been studied by field cycling relaxometry and proton line shape measurements. The dips in theT1 dispersion allowed for the determination of the14N quadrupole coupling tensor. The fact that only one set of14N nuclear quadrupole resonance lines, has been found shows that all N-H groups in nylon-6 are H-bonded. A striking difference in the main line width transition and the low-frequency molecular dynamics has been observed between a slowly cooled “bulk” polyamide-6 sample and a rapidly cooled and highly drawn “fiber” sample by wide line proton nuclear magnetic resonance line shape and spin-lattice relaxation time measurements. This result is consistent with the picture that shearing melt processing procedures, such as spinning, plant stable and long-lived crystallization nuclei into the amorphous phase which impose additional motional constraints on the surroundings and inhibit the self-diffusion process.

Basics of NMR line shape in quasicrystals

The measurement and analysis of broad nuclear magnetic resonance (NMR) spectra of quasicrystals require experimental methods and theoretical interpretations different from NMR investigations of regular periodic crystals. Frequency- and field-sweep methods for recording quasicrystalline NMR spectra are described and compared with the measurement of27Al NMR spectra of icosahedral AlPdMn and decagonal AlNiCo quasicrystals. The nuclear spin interactions that determine the NMR line shape are the same for both types of the above Al-based quasicrystals, where the electric quadrupolar interaction with the broad distribution of its electric field gradient parameters predominantly determines the shape of the broad satellite “background” intensity. The essential observations are an almost isotropic27Al NMR spectrum of the icosahedral quasicrystals and a strong angular dependence of the spectrum of decagonal quasicrystals.

133Cs NMR of the structural phase transition in CsSCN

Abstract The quadrupole perturbed 133Cs ( I = 7 2 ) NMR spectra and the 133Cs 1 2 → − 1 2 spin-lattice relaxation rate T1−1 have been measured in a CsSCN single crystal above and below the cubic-orthorhombic anti-ferroelectric phase transition Tc = 470 K. The strong decrease in T1 on approaching Tc from below demonstrates the onset of large amplitude reorientations of the SCN− groups. In contrast to KSCN and RbSCN domains above Tc. The 133Cs quadrupole coupling constant equals 108 kHz and the asymmetry parameter η is 0.25 at T = 458 K

NMR-melting-curve study of bitumen of different types and origin

The nuclear magnetic resonance (NMR) melting-curve method, employing measurement of the temperature-dependent width of the1H NMR spectrum, was used in a comparative study of softening of various industrial bitumen types (BIT 60 and BIT 90) produced by different manufacturers. Out of three manufacturers involved in the study, only the bitumen samples of one of them exhibited the expected regularity — the NMR melting curves formed two well-defined groups, one belonging to BIT 60-type samples and the other to BIT 90-type, and the BIT 90 samples showed softer melting characteristics. This indicates a reproducible industrial production process and reliable classification into different bitumen types. The NMR melting curves of nominal BIT 60-type samples of the other two manufacturers are scattered irregularly over a large range, extending much beyond the total span of the BIT 60 and BIT 90 curves of the first manufacturer. Hence the classification of these samples into one bitumen type (BIT 60) makes less sense.

ND4 deuteron NMR study of (ND4)4LiD3(SO4)4

Abstract (ND 4 ) 4 LiD 3 (SO 4 ) 4 has been investigated by pulsed Fourier transform ammonium deuteron NMR in the temperature region between 74 and 415 K. At 415 K in the superionic phase the observed lineshape gives a hint for translational diffusion of ND 4 groups. A non-zero ND 4 deuteron line splitting is observed which seems to indicate that the ammonium groups are flipping between two non-equivalent orientations while rotating around more than one axis. Comparison of the experimental data for the splitting with Landau theory shows that the phase transition in (ND 4 ) 4 LiD 3 (SO 4 ) 4 is of second order.

Two-dimensional nuclear magnetic resonance study of phason and amplitudon relaxation mechanisms in structurally incommensurate Rb2ZnCl4

In structurally incommensurate systems phason and amplitudon thermal fluctuations of the frozen-in modulation wave provide for two different nuclear magnetic resonance (NMR) spin-lattice relaxation mechanisms. These two relaxation mechanisms influence different parts of the inhomogeneously broadened NMR absorption spectrum differently. They can be resolved in principle by a conventional one-dimensional measurement of the spin-lattice relaxation time T1 over the NMR lineshape. Here the authors show that a two-dimensional NMR spin-lattice relaxation technique provides a very convenient way of determining the variation of T1 over the lineshape by the use of normalized contour plots. The results for the central transition of 87Rb in Rb2ZnCl4 show that the measured phason-induced spin-lattice relaxation time is temperature-independent. The much less efficient amplitudon relaxation mechanism is bypassed in part by the cross-relaxation process of the amplitudon-relaxed parts to the phason-relaxed parts of the NMR lineshape. The theoretical prediction for the total variation of T1 over the lineshape for the cross-relaxation process agrees with the experimental value of three.