Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Observation of "hidden" magnesium
T2 - first-principles calculations and Mg-25 solid-state NMR of enstatite
AU - Griffin, John M.
AU - Berry, Andrew J.
AU - Ashbrook, Sharon E.
PY - 2011/9
Y1 - 2011/9
N2 - Mg-25 NMR parameters have been determined for two polymorphs of enstatite (MgSiO3), an important magnesium silicate phase present as a major component of the Earth's upper mantle. The crystal structures of both polymorphs contain two crystallographically distinct magnesium sites; however, only a single resonance is observed in Mg-25 MAS NMR spectra recorded at 14.1 and 20.0 T. First-principles calculations performed on geometry-optimised crystal structures reveal that the quadrupolar interaction for the second site is expected to be very large, resulting in extensive broadening of the spectral resonance, explaining its apparent absence in the NMR spectrum. Mg-25 QCPMG NMR experiments employing variable offset cumulative spectroscopy (VOCS) are used to observe the broadened site and enable measurement of NMR parameters. The large difference in quadrupolar interaction between the two crystallographic magnesium sites is rationalised qualitatively in terms of the distortion of the local coordination environment as well as longer-range effects using a simple point charge model. (C) 2011 Elsevier Inc. All rights reserved.
AB - Mg-25 NMR parameters have been determined for two polymorphs of enstatite (MgSiO3), an important magnesium silicate phase present as a major component of the Earth's upper mantle. The crystal structures of both polymorphs contain two crystallographically distinct magnesium sites; however, only a single resonance is observed in Mg-25 MAS NMR spectra recorded at 14.1 and 20.0 T. First-principles calculations performed on geometry-optimised crystal structures reveal that the quadrupolar interaction for the second site is expected to be very large, resulting in extensive broadening of the spectral resonance, explaining its apparent absence in the NMR spectrum. Mg-25 QCPMG NMR experiments employing variable offset cumulative spectroscopy (VOCS) are used to observe the broadened site and enable measurement of NMR parameters. The large difference in quadrupolar interaction between the two crystallographic magnesium sites is rationalised qualitatively in terms of the distortion of the local coordination environment as well as longer-range effects using a simple point charge model. (C) 2011 Elsevier Inc. All rights reserved.
KW - Mg-25 solid-state NMR
KW - First-principles calculations
KW - QCPMG VOCS
KW - Quadrupolar
KW - Enstatite
KW - QUADRUPOLE INTERACTION PARAMETERS
KW - LOW-GAMMA NUCLEI
KW - CHEMICAL-SHIFTS
KW - MAS NMR
KW - NATURAL-ABUNDANCE
KW - O-17 NMR
KW - SILICATE-GLASSES
KW - QCPMG NMR
KW - SPECTROSCOPY
KW - RESOLUTION
U2 - 10.1016/j.ssnmr.2011.08.004
DO - 10.1016/j.ssnmr.2011.08.004
M3 - Journal article
VL - 40
SP - 91
EP - 99
JO - Solid State Nuclear Magnetic Resonance
JF - Solid State Nuclear Magnetic Resonance
SN - 0926-2040
IS - 2
ER -