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ABSTRACT: The recent progress in NMR of glasses is demonstrated using both traditional and improved two-dimensional (2D) NMR techniques. A novel approach for measuring connectivities Qn units in amorphous and polycrystalline solids is explained. Several examples of phosphate samples are presented to show e.g. how chain end groups can be distinguished from pyrophosphate units. Additionally, novel results of 27Al NMR investigations in mullites and Na2O-SiO2-Al2O3 glasses were obtained using a careful lineshape analysis. In mullites three different AlO4 units can be found including an estimation of the relative Al occupancy of the various groups. In ternary Na2O-Al2O3-SiO2 glasses we could prove the presence of two AlO4 sites with Al being surrounded by four Q3 units or possibly one terminal oxygen instead of a Q3 unit (60 ppm) and by four Q4 groups (53 ppm). Finally, two different Na sites have been detected for the first time using 23Na MQ NMR in a glass 22.7 Na2O 0.7 B2O 69.8 SiO2.
Berichte der Bunsengesellschaft für physikalische Chemie. 05/2010; 100(9):1560 - 1562.
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ABSTRACT: The structure of various hydrated and untreated glasses of the system Na2O-B2O3-SiO2 was investigated using multinuclear NMR. Two different BO4 units have been detected by 11B SATRAS (Satellite Transition Spectroscopy) NMR. Comparing the spectra of the untreated and hydrated glasses it was found, that nearly all BO3, units and one of the BO4 units are removed during the reaction of the glasses with hydrous solution. Furthermore, 1H-11B REDOR (Rotational Echo Double Resonance) has been used to investigate the incorporation of protons in the hydrated glasses. New aspects containing the structural role of protons are obtained.
Berichte der Bunsengesellschaft für physikalische Chemie. 05/2010; 100(9):1655 - 1657.
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ABSTRACT: 2H NMR spectra of dimethylsulfone were measured with noise excitation and solid echo NMR spectroscopy in the temperature range from 125 to 355 K. Besides the known fact that broad NMR spectra can be measured with both methods, in comparable times it is shown that for noise excitation, the signal loss is negligible compared to echo spectroscopy in the regime when the correlation times of the motions are of the order of magnitude of the echo pulse spacing. For simulating the dynamic NMR spectra acquired with noise excitation, only the motional process must be taken into account and relaxation can be neglected. Furthermore, the problem of restricted acquisition bandwidth in noise NMR spectroscopy is discussed.
Solid State Nuclear Magnetic Resonance 07/2000; 16(3):123-30. · 1.71 Impact Factor
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ABSTRACT: A simple two-dimensional correlation experiment that enables determination of through-bond connectivity in the solid state is described. The experiment is performed under fast magic angle spinning (MAS) conditions. After the initial pi/2 pulse, the magnetization develops freely under the MAS Hamiltonian. The t1-period is followed by a strong spin locking pulse used as mixing period. The dipolar coupling is averaged out by magic angle spinning, and the chemical shifts and r.f.-offsets are scaled by the applied spin locking field. Hence, for strong locking conditions, the isotropic J-coupling is the dominant interaction. The mixing Hamiltonian is thus identical to the well-known TOCSY-Hamiltonian, resulting in a net through-bond magnetization transfer. The mixing-time dependence of the exchange rates is investigated. Applications to crystalline P4S7 and MgP4O11 are shown.
Solid State Nuclear Magnetic Resonance 07/2000; 16(3):189-97. · 1.71 Impact Factor
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ABSTRACT: A two-dimensional correlation experiment is described, in which homonuclear dipolar couplings are used to realize through-space magnetization exchange on spin-1/2 (31P) and on quadrupolar nuclei (23Na and 11B). In the detection period, Magic Angle Spinning is applied to enhance resolution, and the dipole couplings are re-introduced in the mixing period by spinning off the Magic Angle. The dependency of the exchange rates on the mixing time and the spinning angle is investigated. The influence of strong spin-locking during mixing is discussed, and shown in the spin-1/2 case to remove the dependence on chemical shift offset effects. For quadrupolar spins, the experiment yields information on the relative tensor orientations of the coupled quadrupoles. Applications to crystalline sodium aluminum diphosphate, sodium sulphite, and potassium borate glasses are shown.
Solid State Nuclear Magnetic Resonance 06/1999; 13(4):245-54. · 1.71 Impact Factor
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Phosphorus Research Bulletin 01/1999; 10:6.
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ABSTRACT: 31P double quantum (DQ) NMR is used for improved studies of the structure of phosphate glasses. The common Qn notation of the network forming tetrahedral phosphate units with n bridging oxygen atoms is extended to Qn,jkl indicating the Q type of the bonded adjacent units by the additional superscripts j,k and l. It will be shown that: (i) Q1 units have different isotropic chemical shifts depending on whether they form diphosphate anions in the amorphous state (Q1,1) or end groups of chains (Q1,2) and (ii) that even Q2 units possess different isotropic chemical shifts such that in the DQ dimension Q2,11 can be distinguished from Q2,12 and middle groups of longer chains or rings (Q2,22). Based on this result the opportunity for measuring chain length distributions in the amorphous state is discussed and first results for binary calcium phosphate glasses are presented. The advantages and also the limitations of this novel approach will be discussed.
Solid State Nuclear Magnetic Resonance 01/1999; 13(3):189-200. · 1.71 Impact Factor
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ABSTRACT: 31P multiple-quantum solid-state NMR spectroscopy is introduced as a new approach for elucidating internuclear distances between phosphorus nuclei in phosphates. The typical shorter distance between chemically bound groups allows the determination of the chemical network. The method is superior to 31P exchange experiments, which, in principle, provide similar information. Separation of two crystalline Mg2P2O7 phases is observed by both methods, but the double-quantum experiment gives further information of couplings between sites with equal isotropic chemical shifts. In Ca2P6Ol7, which contains Q2 and Q3 groups with large chemical shift anisotropies, the connectivities can be deduced from the double-quantum experiment due to different cross-peak intensities. Our results are in good agreement with X-ray diffraction measurements and suggest applications to other, more complicated phosphates.
10/1996;
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ABSTRACT: The magic-angle spinning sidebands of the satellite transition (ST, m = +/- 3/2 <==> +/- 1/2) for 11B nuclear magnetic resonance (11B ST spectroscopy) have been used to detect multiple boron sites in Na2O-B2O3-SiO2 glasses. The experimental details and data analysis are described, how multiple BO4 and BO3 units can be distinguished using standard magic-angle spinning. For a 16Na2O-30B2O3-53.9SiO2 glass (0.1 MnO) two BO4 units with chemical shifts of -2.5 and 0 ppm were found which differ considerably in their quadrupole interaction. Besides this we found three different BO3 units with approximate chemical shifts of 17, 15, and 19 ppm. The results are compared with earlier measurements.
Solid State Nuclear Magnetic Resonance 11/1995; 5(1):51-61. · 1.71 Impact Factor
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ABSTRACT: 27Al Nuclear magnetic resonance (NMR) satellite transition spectroscopy has been used for the quantitative investigation of the microstructure of polycrystalline 2/1-type mullite (approximately 76 wt.-% Al2O3 and 24 wt.-% SiO2). Using this method the chemical shifts, quadrupole interaction parameters and relative amount of Al in the various coordination polyhedra have been obtained with high accuracy. The additional suppression of second-order quadrupolar broadening of the 27Al magic-angle spinning (MAS) spinning sidebands of the inner satellite transitions allows three different AlO4 units to be detected. The three AlO4 resonances with isotropic chemical shifts at 68, 53 and 45 ppm are associated with AlO4 polyhedra in the tetrahedral double chains [AlO4(T)], the tetrahedra adjacent to the oxygen vacancies [AlO4(T*)] and the tetrahedra AlO4(T') linked by Oc* with AlO4(T*), respectively. Our NMR study of a polycrystalline sample supports the results of previous single-crystal studies of Angel et al. [Am. Mineral., 76 (1991) 332], especially the exclusion of silicon from the tetrahedral sites linked by Oc*.
Solid State Nuclear Magnetic Resonance 10/1994; 3(5):241-8. · 1.71 Impact Factor
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ABSTRACT: 27Al Satellite transition spectroscopy (SATRAS) has been used to extract both the quadrupole interaction and its distribution width from MAS spectra of glasses. Using this method a measurement at a single magnetic field strength allows one to obtain the true chemical shifts and the quadrupole interaction (and its distributions) with high accuracy, including quantification of the results. In contrast to earlier investigations the central transition MAS lineshapes can be described without assumptions and give correct relative proportions of differently coordinated Al species in glasses. The distribution model for the quadrupole interaction and the resulting MAS lineshapes are discussed in detail including a description of the experimental requirements. Experimental results of 27Al SATRAS spectra of a ternary Al2O3-B2O3-P2O5 glass exhibiting 4-, 5-, and 6-coordinated aluminum species clearly prove different mean values and distribution widths for the quadrupole interaction in the various AlOx polyhedra.
Solid State Nuclear Magnetic Resonance 05/1993; 2(1-2):73-82. · 1.71 Impact Factor
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ABSTRACT: 27Al NMR spectra of polycrystalline aluminum borate 9Al2O3.2B2O3 have been measured at 104, 130 and 156 MHz. The parameters of the quadrupole interaction and the isotropic chemical shifts have been obtained by fitting the CT/MAS pattern and consideration of the inner satellite transitions m = 3/2<-->1/2 and m = - 1/2<-->- 3/2. The gain in spectral resolution concerned with the observation of the MAS lines of the inner satellites leads to complete separation of the signals of AlO6, AlO5 and AlO4 polyhedra. Also signals of structural groups of one and the same coordination number can be distinguished. Experimental and theoretical lineshape calculations are compared.
Solid State Nuclear Magnetic Resonance 12/1992; 1(5):261-6. · 1.71 Impact Factor
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ABSTRACT: 31P MAS NMR has been used to determine 31P chemical shift tensors of crystalline silicon phosphates. The chemical shift data of five polymorphs of SiP2O7 (hexagonal, tetragonal, cubic and two monoclinic forms) are presented besides those of Si3(PO4)4. Results of 31P 2D exchange NMR on a phase mixture of different silicon diphosphates are shown. This novel approach allows an unambiguous identification of the various phases even in multicomponent mixtures as occurring in ceramics.
Chemical Physics Letters 258:107-112. · 2.34 Impact Factor
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ABSTRACT: Double quantum nuclear magnetic resonance measurements exploiting the dipole coupling between the phosphorus atoms as well as a novel two-dimensional exchange experiment using the scalar coupling are described for measuring the connectivities of phosphate tetrahedra in glasses. It is shown that bonding scenarios of up to four connected tetrahedra can be determined in phosphates and phosphate glasses and that estimations of the chain length distributions are possible in glasses having shorter chain fragments. Nuclear magnetic resonance (NMR) is also capable of measuring local order in extruded phosphate glasses using rotorsynchronized excitation in combination with magic angle sample spinning. Finally, we show that the relative orientations of chemical shift tensors can be determined by two-dimensional nuclear magnetic resonance. This determination provides an additional verification of connectivities and can possibly enable access to bonding angle data in the future.
Journal of Non-Crystalline Solids · 1.54 Impact Factor
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ABSTRACT: The glass structure in two ternary systems was investigated with respect to their applicability as electrode glasses. For Na2O–Al2O3–SiO2 glasses, a good pNa electrode signal is observed if (i) AlO−4 units exist, linked mainly to Q4m units (Qnm: silicate tetrahedra, n: number of Si–O–Si bridges, m: number of Si–O–Al bridges), (ii) some other AlO−4 units are bonded to mainly Q3m units and (iii) the condition 2>Q4m/Q3m>1 holds. In Na2O–B2O3–SiO2 glasses, a pNa signal is measured if the ratio of the BO−4 units linked to BO3 or to Q4 is less than 1. Two-dimensional double quantum nuclear magnetic resonance (DQ NMR) spectroscopy has been applied to 29Si enriched sodium silicate glasses for measuring the connectivities of the Qn units (m=0), enabling improved studies of the medium range order. We are able, for the first time, to distinguish between the various Q3 and Q4 units bonded to different numbers of Q3 and/or Q4 groups.
Journal of Non-Crystalline Solids · 1.54 Impact Factor
