Nuclear magnetic resonance at high temperature

Stebbins, Jonathan F.

doi:10.1021/cr00007a004

Cited by 77 publications

(49 citation statements)

References 82 publications

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“…High temperature static experiments were carried out with a home-built horizontal solenoid probe capable of temperatures greater than 1300 ~ C (Stebbins 1991). Room temperature magic-angle spinning (MAS) experiments were carried out with a 5 mm high-speed MAS probe at a spinning speed of 10 kHz (Doty Scientific, Inc.), and high temperature MAS experiments were carried out with a 7 mm high-temperature MAS probe at spinning speeds of 2.5-3.5 kHz (Doty Scientific, Inc.).…”

Section: Experimental Methodsmentioning

confidence: 99%

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

1992

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Abstract. Relaxation times (T1) and lineshapes were examined as a function of temperature through the c~-// transition for z9si in a single crystal of amethyst, and for 29Si and 170 in cristobalite powders. For single crystal quartz, the three z9Si peaks observed at room temperature, representing each of the three differently oriented SiO, tetrahedra in the unit cell, coalesce with increasing temperature such that at the c~-//transition only one peak is observed. 29Si Tl's decrease with increasing temperature up to the transition, above which they remain constant. Although these results are not uniquely interpretable, hopping between the Dauphin6 twin related configurations, el and ez, may be the fluctuations responsible for both effects. This exchange becomes observable up to 150~ below the transition, and persists above the transition, resulting in//-quartz being a time and space average of el and e2. 298i Tl's for isotopically enriched powdered cristobalite show much the same behavior as observed for quartz. In addition, 170 Tl's decrease slowly up to the e-// transition at which point there is an abrupt 1.5 order of magnitude drop. Fitting of static powder ~70 spectra for cristobalite gives an asymmetry parameter (t/) of 0.125 at room T, which decreases to <0.040 at the transition temperature. The electric field gradient (EFG) and chemical shift anisotropy (CSA), however, remain the same, suggesting that the decrease in t/is caused by a dynamical rotation of the tetrahedra below the transition. Thus, the mechanisms of the e-// phase transitions in quartz and cristobalite are similar: there appears to be some fluctuation of the tetrahedra between twin-related orientations below the transition temperature, and the//-phase is characterized by a dynamical average of the twin domains on a unit cell scale.

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Section: Experimental Methodsmentioning

confidence: 99%

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

1992

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“…The in situ high temperature (up to 1400°C) 27 Al NMR experiments were performed using a Varian 'Infinity+' 400 (9.4 T) spectrometer operating at 104.17 MHz with a home-built static probe [39]. A molybdenum 2-turn solenoidal radio frequency coil was designed to fit closely around hexagonal boron nitride sample containers, which had 8.4-mm diameters and 16.8-mm lengths.…”

Section: High Temperature Nmrmentioning

confidence: 99%

In situ high temperature 27Al NMR study of structure and dynamics in a calcium aluminosilicate glass and melt

Kanehashi

Stebbins

2007

Journal of Non-Crystalline Solids

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“…Chemical shifts were referenced to room temperature 1.0 M solutions of Al(NO3)3, NaC1, and NaF for 27A1, 23Na, and 19F, respectively. High temperature static powder spectra were collected using a home-built, resistively heated, horizontal solenoid probe capable of temperatures greater than 1300~ (Stebbins 1991). Sample temperatures were calibrated against the furnace control thermocouple in a separate non-NMR high temerature run in which a thermocouple was placed inside a boron nitride sample container filled with A1203 powder.…”

Section: Nmr Spectroscopymentioning

confidence: 99%

Diffusion and the dynamics of displacive phase transitions in cryolite (Na3AlF6) and chiolite (Na5Al3F14): Multi-nuclear NMR studies

1994

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Abstract.Cryolite is a mixed-cation perovskite (Na2(NaA1)F6) which undergoes a monoclinic to orthorhombic displacive phase transition at ~ 550 ~ C. Chiolite (NasA13F14) is associated with cryolite in natural deposits, and consists of sheets of corner sharing [A1F6] octahedra interlayered with edge-sharing [NaF6] octahedra. Multi-nuclear NMR line shape and relaxation time (T1) studies were performed on cryolite and chiolite in order to gain a better understanding of the atomic motions associated with the phase transition in cryolite, and Na diffusion in cryolite and chiolite. 27A1, 23Na, and 19F static NMR spectra and Tl's in cryolite suggest that oscillatory motions of the [A1F6] octahedra among four micro-twin and anti-phase domains in e-cryolite begin at least 150 ~ C below the transition temperature and persist above it. Variable temperature 23Na MAS NMR further indicates diffusional exchange at a rate of at least 13 kHz between the Na sites by the time the transition temperature is reached. 27A1 and 23Na Tl'S show the same behavior with increasing temperature, indicating the same relaxation mechanisms are responsible for both. The first order nature of the cryolite transition is apparent as a jump in the 23Na and 27A1 Tl's. Above the transition temperature, the TI'S decrease slightly indicating that the motions responsible for the drop in T 1 are still present above the transition, further supporting the dynamic nature of the high temperature phase of cryolite. Chiolite 23Na static spectra decrease in linewidth with increasing temperature, indicating increased Na diffusion, which is interpreted as occurring within the [NaF6] sheets in the chiolite structure, but not between the two different Na sites. 27A1 and 23Na Tl's show similar behavior as in cryolite, but there is no discontinuity due to a phase transition. 19F TI's are constant from room temperature to 150 ~ C indicating no oscillatory motion of the [A1F6] octahedra in chiolite.

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Nuclear magnetic resonance at high temperature

Cited by 77 publications

References 82 publications

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

In situ high temperature 27Al NMR study of structure and dynamics in a calcium aluminosilicate glass and melt

Diffusion and the dynamics of displacive phase transitions in cryolite (Na3AlF6) and chiolite (Na5Al3F14): Multi-nuclear NMR studies

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