27Al double-rotation NMR study of Al2SiO5 polymorph minerals

²⁷Al double-rotation (DOR) NMR spectra of the alumino-silicate polymorph minerals, kyanite, sillimanite and andalusite, show separately resolved peaks, relating to the crystallographically non-equivalent sites. The isotropic chemical shifts are calculated from the observed peak positions and they correlate closely with those found previously by simulations of MAS NMR spectra. The intensities of the four non-equivalent sites in kyanite are found to have an exponential relationship with their corresponding quadrupolar coupling constants (C _Q ).     

Solid-state 27Al NMR studies of aluminophosphate molecular sieves. Enhanced resolution by quadrupole nutation and double-rotation.

Solid-state 27Al NMR spectra of several aluminophosphate molecular sieves have been recorded with conventional magic-angle spinning (MAS), double-rotation (DOR) and quadrupole nutation with fast MAS. Enhanced resolution was obtained in the quadrupole nutation experiment at certain radiofrequency pulse strengths. This extra resolution can be comparable to that attainable using DOR, and does not introduce spinning sidebands.     

71Ga,27Al and23Na solid state MAS NMR of β- and β″-aluminogallates

Two series of compounds with sodium β- and β″-alumina structure have been studied in which the aluminium is partly replaced by gallium. The level of substitution has been varied fromx(Ga/Ga+Al)=0.3 to 0.8. The approximately quantitative analysis of aluminium and gallium NMR of these aluminogallates has allowed us to determine a gallium site occupancy for the different values ofx. For sodium, several sites have been shown and a correlation between gallium substitution and sodium positioning has been proposed. The structures are affected by the changes in cation size from aluminium to gallium. The sites occupancy has been determined and allows one to understand the distortions, due to gallium insertion, in the structures.     

27Al and 65Cu NMR study in UCu5Al.

We have studied the microscopic properties of the tetragonal UCu₅Al Kondo compound by ²⁷Al and ^63,65Cu NMR in the paramagnetic state. NMR and susceptibility measurements performed on the powdered sample, but oriented along the applied field, showed χ>χ. Plots of K(T) against χ(T) at temperatures T≥100 K yield the transferred hyperfine fields of +5.9 kOe/μ_B for ²⁷Al nuclei, and +5.3 and −7.0 kOe/μ_B for ⁶⁵Cu nuclei in crystallographically inequivalent Cu(2) and Cu(1) sites, respectively. The Knight shift vs. susceptibility plots for T<100 K exhibit a deviation from the linear behaviour (absolute values of shifts become smaller than expected). We attribute this finding to the crystalline electric field effect in similar way as it was reported for several Ce-based compounds. The random distribution of the Al and Cu(2) atoms in the crystal lattice we consider as a reason of an unusual broadening of the NMR spectra, particularly at low temperatures.     

27Al NMR study in ZrNiAl

We have studied the microscopic properties of the hexagonal ZrNiAl, a model compound for a wide family of intermetallic compounds crystallizing in this type of structure, by using ²⁷Al NMR spectroscopy. We have investigated the lineshape of static and MAS NMR spectra as a function of magnetic field strength (4.7–9.4 T) and temperature (5–300 K). Our data indicate that the ²⁷Al NMR spectra result from a combined effect of quadrupole and anisotropic shift interactions. The ²⁷Al nuclei are in an environment characterized by the quadrupole coupling constant e²qQ/h of 3.3 MHz, asymmetry parameter η_Q of 0.42, isotropic shift δ_iso of 393 ppm, shift anisotropy δ_anis = δ_zz − (δ_xx + δ_yy)/2 of 150 ppm, and asymmetry factor η_S of 0.5. They are found to be temperature independent. The spin–lattice relaxation rate measured at 7.05 T is proportional to the temperature with T₁T = 135 s K. The mechanisms responsible for observed values of δ_iso, δ_anis, T₁T, and the enhanced Korringa constant are discussed.     

27Al NMR study in UNiAl

The ternary compound UNiAl exhibiting an antiferromagnetic order below T_N = 19.3 K has been studied in the paramagnetic state using the ²⁷Al NMR technique and different magnetically oriented samples. The quadrupole coupling constant e²qQ/h = 1.56 MHz is temperature independent. The dominant, longitudinal component of the Knight shift with respect to the hexagonal c axis, K, is positive and increases upon lowering the temperature down to 50 K. Much smaller in magnitude, the transverse component, K_±, is also positive and only slightly temperature dependent. The plots of the Knight shift vs magnetic susceptibility K(χ) and K_±(χ_±) form the same line, which implies that the transferred hyperfine field of 9.2 kOe/μB for ²⁷Al nuclei should be considered isotropic.     

27Al NMR spectroscopy of minerals and related materials

We present a review of the applications of²⁷Al NMR methods to investigations of the structures of minerals, primarily alumino-silicates, and related synthetic compounds. Such materials are ubiquitous in the earth and other terrestrial planets. Because of their diverse structures and compositions, they also provide examples of many situations in which²⁷Al NMR spectroscopy can provide useful information. Thus, they serve well as model compounds for synthetic crystalline and amorphous materials and usefully illustrate the applications of many techniques. The advent of high-field superconducting magnets (H ₀>9 T) has made application of²⁷Al NMR to solids much more effective than it was previously, and we focus primarily on these recent applications but also discuss older, single-crystal data.²⁷Al NMR methods can be used for many purposes in investigations of solids. Here we emphasize the following. 1) Determination of the Al coordination number and the polymerization of tetrahedrally coordinated Al. 2) Determination of tetrahedral Al/octahedral Al ratios. 3) Investigation of tetrahedral Al, Si order/disorder in, especially, framework-structure alumino-silicate phases. 4) Investigation of the static structural changes and dynamical behavior of crystals undergoing structural phase transitions. 5) Investigation of the local symmetry of Al-sites through the quadrupole coupling constant and asymmetry parameter.     

Fullerene local order in Na2CsC60 by23Na NMR

We have investigated the alkali metal fulleride Na₂CsC₆₀ by²³Na nuclear magnetic resonance (NMR), The NMR line of the tetrahedral site is split below 170 K (T and T′ lines) similarly to the A₃C₆₀ compounds with A=Rb or K. The intensity fraction of the T′ line follows the same temperature dependence as the¹³C NMR line width. We have also found that the spectrum is independent of the cooling rate. Spin-echo double resonance measurements show that T and T′ sites are mingled on a microscopic scale. We propose that the different²³Na NMR lines correspond to different fullerene orientational environments of the tetrahedral alkaline site.     

Double rotation27Al NMR in molecular sieves

Although high-resolution NMR spectra can be obtained in solids, the use of²⁷Al NMR to investigate the structure of aluminosilicate and aluminophosphate molecular sieves has been severely limited because anisotropic second-order quadrupolar interactions, responsible for spectral broadening, cannot be eliminated by conventional magic angle spinning (MAS) or multiple pulse techniques. Here we give the principles of the double rotation (DOR) NMR technique which can remove not only the first-order broadenings but also the second-order broadenings in the NMR spectra of quadrupolar nuclei in solids. High-resolution²⁷Al NMR using DOR is capable of resolving discrete framework aluminum sites in aluminophosphate molecular sieves, permitting quantitative investigation of site-specific adsorbate-host interactions, and of discriminating different aluminum species in zeolites.     

<Superscript>23</Superscript>Na and <Superscript>27</Superscript>Al NMR Study of Structure and Dynamics in Mordenite

Temperature dependencies of ²⁷Al and ²³Na nuclear magnetic resonance spectra and spin–lattice relaxations in mordenite have been studied in static and magic angle spinning regimes. Our data show that the spin–lattice relaxations of the ²³Na and ²⁷Al nuclei are mainly governed by interaction of nuclear quadrupole moments with electric field gradients of the crystal, modulated by translational motion of water molecules in the mordenite channels. At temperatures below 200 K, the dipolar interaction of nuclear spins with paramagnetic impurities becomes an important relaxation mechanism of the ²³Na and ²⁷Al nuclei.     

Removal of sidebands in double-rotation NMR in real time

Double-rotation (DOR) is the only technique generally capable of yielding high-resolution NMR spectra of half-integer quadrupolar nuclei in one dimension for solids without the need for sophisticated coherence pathway selection. Unfortunately, due to the low outer rotor spinning frequencies currently available, the spectra often contain a large number of spinning sidebands which may overlap with the resonances of interest. We implement a simple, robust, and easy to use family of pulse sequences, which in practice are fully analogous to the 'total suppression of sidebands' (TOSS) sequences, to suppress all sidebands arising from the spinning of the outer rotor in DOR experiments. By removing the rotor phase dependence of the evolution of the sidebands, the sidebands destructively interfere with one another during the course of signal averaging to yield 'solution-like' spectra of half-integer quadrupolar nuclei in solids. Advantages and shortcomings of the method compared to other DOR sideband suppression methods are explored with the aid of simulations.     

Absolute quantification of Na+ bound fraction by double-quantum filtered 23Na NMR spectroscopy

A method is described for the absolute quantification of double-quantum filtered spectra of spin-3/2 nuclei ((23)Na). The method was tested on a model system, a cationic exchange resin for which the number of Na(+) binding sites was quantitatively controlled. The theoretical and experimental approaches were validated on samples with different Na(+) concentrations. An excellent agreement between the results obtained by double-quantum and single-quantum acquisitions was found. This method paves the way for absolute quantification of both bound and free fractions of Na(+), which are determining factors in the characterization of salted/brined/dried food products.     

活体23Na NMR及在生物医学中的应用

胞内Na⁺浓度和跨膜梯度的维系对于保持组织细胞的正常生理状态具有重要的作用.本文详细介绍了生物组织细胞内Na⁺测定的²³Na NMR方法,并讨论了²³Na NMR在生理病理学研究和疾病诊断等生物医学领域内的应用。     

23Na and (1)H NMR microimaging of intact plants

(23)Na NMR microimaging is described to map, for the first time, the sodium distribution in living plants. As an example, the response of 6-day-old seedlings of Ricinus communis to exposure to sodium chloride concentrations from 5 to 300 mM was observed in vivo using (23)Na as well as (1)H NMR microimaging. Experiments were performed at 11.75 T with a double resonant (23)Na-(1)H probehead. The probehead was homebuilt and equipped with a climate chamber. T(1) and T(2) of (23)Na were measured in the cross section of the hypocotyl. Within 85 min (23)Na images with an in-plane resolution of 156 x 156 micrometer were acquired. With this spatial information, the different types of tissue in the hypocotyl can be discerned. The measurement time appears to be short compared to the time scale of sodium uptake and accumulation in the plant so that the kinetics of salt stress can be followed. In conclusion, (23)Na NMR microimaging promises great potential for physiological studies of the consequences of salt stress on the macroscopic level and thus may become a unique tool for characterizing plants with respect to salt tolerance and salt sensitivity.     

NMR of23Na in small particles of ferroelectric NaNO2

Pulse and wide line NMR spectroscopy were applied to small ferroelectric NaNO₂ particles, produced from aqueous solution and embedded loosely in silicagel. Mean particle diameters as determined by SEM and TEM were between 0.2 and 5.0 µm. From the cw-experiments it followed, that the particles had the crystalline structure of the bulk. It is shown that the spectrum of critical fluctuations and the phase transition temperature in the particles proved to be independent of the size. If there is a dead layer at the particle surfaces its thickness does not exceed 1×10^–2µm.     

Influence of sodium ion dynamics on the 23Na quadrupolar interaction in sodalite: a high-temperature 23Na MAS NMR study

High-temperature ²³Na MAS NMR experiments up to 873 K for a number of different sodalites (Na₈[AlSiO₄]₆(NO₃)₂, Na₈[AlSiO₄]₆(NO₂)₂, Na₈[AlSiO₄]₆I₂, Na_7.9[AlSiO₄]₆(SCN)_7.9 · 0.5H₂O, Na₈[AlGeO₄]₆(NO₃)₂, and Na₇[AlSiO₄]₆(H₃O₂) · 4H₂O) were carried out. The spectra of the first five sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate sodalite, the nitrate aluminosilicate, and germanate sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydrosodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the sodalite β-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites.     

Application of27Al NMR techniques to structure determination in solids

There have been great improvements in the quality of²⁷Al NMR spectra from solids over the last decade. The impact of this technique on structure determination for a wide range of solids is briefly reviewed. Emphasis is placed on the effects arising from the presence of the quadrupolar interaction and strategies that allow unambiguous spectral interpretation. It is demonstrated that in addition to the chemical shift, the quadrupolar interaction itself can be a rich source of local information about solids. The insight obtained from²⁷Al NMR into atomic level structure often contains surprises, such that previous models of structure and properties have to be reassessed.     

23Na TQF NMR imaging for the study of spinal disc tissue

A method for acquiring triple quantum filtered (TQF) (23)Na NMR images is proposed that takes advantage of the differences in transverse relaxation rates of sodium to achieve positive intensity, PI, NMR signal. This PITQF imaging sequence has been used to obtain spatially resolved one-dimensional images as a function of the TQF creation time, tau, for two human spinal disc samples. From the images the different parts of the tissue, nucleus pulposus and annulus fibrosus, can be clearly distinguished based on their signal intensity and creation time profiles. These results establish the feasibility of (23)Na TQF imaging and demonstrate that this method should be applicable for studying human disc tissues as well as spinal disc degeneration.     

23Na NMR evidence for charge order and anomalous magnetism in NaxCoO2

Oriented powder samples of NaxCoO2 are studied by 23Na NMR and SQUID magnetometry. In nominal 0.50相似文献