Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ASSOC MINERALOGICAL SCIENCES  

Enstatite (MgSiO3) sample was prepared by conventional solid state reaction at 1500 degrees C, followed by cooling to ambient temperature with different cooling rates (0.04-500 degrees C/s). Quantitative analysis of enstatite phases in the samples by Rietveld refinement and Si-29 MAS NMR revealed that a large amount of metastable protoenstatite (30-40 mol%) along with clinoenstatite was preserved in all samples. The presence of protoenstatite was also confirmed by micro-Raman spectroscopy. The crystal structures of protoenstatite and clinoenstatite at room temperature were refined using the Rietveld method, and were essentially the same as those reported by previous studies. As the solid state reaction method is commonly used to prepare synthetic clinoenstatite, the present result implies that the 'clinoenstatite' starting materials used in previous phase equilibrium studies of MgSiO3 pyroxene might contain overlooked protoenstatite, which could affect the interpretation for phase transition and thus those results should be reexamined.

DOI： 10.2465/jmps.170616

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The crystal structures of Ca(Al0.5Si0.5)O-2.75 and Ca(Al0.4Si0.6)O-2.8 ordered oxygen-deficient perovskite phases are synthesized at 7 and 11 GPa, respectively, and 1500 A degrees C, and were studied using NMR and synchrotron powder X-ray diffraction. Si-29 MAS NMR, Al-27 MAS and 3Q MAS NMR measurements revealed a single tetrahedral Si and single octahedral Al peak for the Ca(Al0.5Si0.5)O-2.75 phase, and a tetrahedral and an octahedral Si peak and a single octahedral Al peak for the Ca(Al0.4Si0.6)O-2.8 phase. Using this structural information as constraints, the crystal structures were solved from synchrotron X-ray diffraction data by the structure determination from powder diffraction (SDPD) technique. To double-check the structures, first-principles calculations of NMR parameters (chemical shifts and electric field gradients) were also conducted after relaxing the obtained structures. The calculated NMR parameters of both phases are consistent with the observed NMR spectra. The crystal structures of both phases consist of a perovskite-like layer of (Al,Si)O-6 octahedra and a double-layer of SiO4 tetrahedra that are stacked alternatively in the [111] direction of ideal cubic perovskite. The perovskite-like layer is made of a double-layer of Al octahedra for the Ca(Al0.5Si0.5)O-2.75 phase, and a triple-layer with a Si octahedral layer sandwiched between two Al octahedral layers for the Ca(Al0.4Si0.6)O-2.8 phase. A unique feature common to both structures is that each SiO4 tetrahedron has one terminal oxygen that is not shared by other Si or Al. Homologous relation among these phases and merwinite (Ca3MgSi2O8) in terms of different numbers (1-3) of octahedral layers within the perovskite-like layer is noted.

DOI： 10.1007/s00269-017-0896-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

The presence of water (hydrogen) in nominally anhydrous mantle minerals may have profound effects on their physical properties (e.g., electrical conductivity, diffusivity, rheology), and these effects are expected to depend on how water is incorporated in the crystal structure. For olivine, the most abundant upper mantle mineral, despite extensive studies, mostly using vibrational spectroscopy, the interpretations are still not well constrained. To provide better understanding on this issue, we carried out a comprehensive H-1 and Si-29 NMR study on an Mg2SiO4 forsterite sample containing about 0.5 wt% H2O synthesized at 12 GPa and 1200 degrees C, complemented by Raman measurement and first-principles calculation of the geometry, stability, and NMR parameters of model structures. The Raman spectra contain relatively sharp O-H stretching bands near 3612, 3579, and 3567 cm(-1) and a broader band near 3547 cm(-1), similar to previous reports. The H-1 static and MAS NMR data revealed that there are two main populations of protons in the hydrous forsterite structure, one experiencing strong (H-1H)-H-1 homonuclear dipolar couplings and contributing to a broad peak near 2.4 ppm, and another with weaker dipolar couplings and contributing to a narrower peak near 1.2 ppm in the MAS NMR spectrum at 30 kHz. Two-dimensional H-1 CRAMPS-MAS NMR measurements confirmed that the two proton components belong to the same phase and the contrast in MAS NMR peak width is largely due to difference in the strength of H-1-H-1 homonuclear dipolar couplings. In addition, there is also a very weak, narrow H-1 MAS NMR peak near 7.3 ppm (contributing to < 0.1% of the total intensity) due to protons that are more remote from the two main components. First-principles calculation confirmed that the two main proton components can be attributed to the hydrogarnet-like substitution mechanism of four H ions for one Si [(4H) Si] in a tetrahedral site of olivine, but unlike hydrogarnet with one of the protons pointing away from the tetrahedral center and located in an adjacent interstitial site, thus experiencing weaker dipolar couplings than those in the vicinity of the vacant tetrahedron; the very weak narrow peak near 7.3 ppm can be attributed to the substitution mechanism of two H ions for one Mg in an M1 site [(2H)M-1] of forsterite. The H-1-Si-29 CP-MAS NMR spectra revealed both a broad peak encompassing the position for OH defect-free forsterite (-61.7 ppm) and a narrower peak at higher frequency (-60.9 ppm). First-principles calculation indicates that these peaks are accountable by the same models as for the H-1 NMR data. Thus, this study has provided unambiguous evidence supporting that hydrogen is incorporated in forsterite at relatively high-pressure dominantly as (4H) Si defects, with (2H) M1 defects playing only a very minor role. The much larger H-1 chemical shift for protons associated with the latter (than the former) is correlated with stronger hydrogen bonding for the latter, which in turn reflects difference in bonding environments of the OH groups (with the latter bonded to a Si, and the former only bonded to Mg). Similar correlation applies to the O-H stretching frequency.The (4H) Si defects are responsible for the observed high-frequency O-H stretching bands (> 3450 cm(-1)), and the (2H) M1 defects give lower frequencies (undetected here due to low abundance, but most likely near 3160-3220 cm(-1) as previously reported) in vibrational spectra. These results can serve as a guide for (re-) interpretation of infrared and Raman spectroscopic data on hydrous olivine produced under different pressure and silica activity conditions, and require reconsideration of any models for the effects of water on physical properties of olivine based on different interpretations of such data. This study also demonstrated the usefulness of the combined solid-state NMR and first-principles calculation approach in unraveling the hydrogen incorporation mechanisms in nominally anhydrous minerals.

DOI： 10.2138/am-2017-5878

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In order to clarify cation distributions in the M1 and M2 sites of (Mg,Zn)(2)SiO4 olivine solid solution, Si-29 MAS NMR spectroscopic measurement and first-principles NMR parameter calculation were conducted. The Si-29 MAS NMR spectra of (Mg0.95Zn0.05)(2)SiO4 and (Mg0.90Zn0.10)(2)SiO4 olivine samples reveled three new peaks at relative chemical shift differences of 0.2, 1.1 and 2.3 ppm from the main peak of forsterite (-61.8 ppm). These shifts can be attributed to changes in the second-nearest-neighbors of Si due to substitution of Mg by Zn. Based on first-principles calculations, these peaks can be assigned to the following three groups of local Si environments in the order of increasing shift from the main peak of forsterite: i) Si tetrahedra with one corner-shared Zn in M1 or M2 octahedron, ii) Si tetrahedra with one edge-shared Zn in M2 octahedron, and iii) Si tetrahedra with one edge-shared Zn in M1 octahedron. Since the last two peaks are well separated from the others, the relative abundances of Zn in the M1 and M2 sites can be quantified using these peaks. Preference of Zn for M1 site over M2 site was inferred from the observed peak intensities. The present study demonstrated the usefulness of 29Si MAS NMR spectroscopy for quantitatively studying cation distributions in solid solutions.

DOI： 10.2465/jmps.151104a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by Al-27-H-1 cross polarization and quantitative H-1 MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its H-1 NMR partial spectrum was derived from the Al-27-H-1 cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative H-1 NMR spectra. The degree of aluminum avoidance and the relative tendency for Si-O-Si, Si-O-Al and Al-O-Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al-O-Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84-89% and 68-78%, respectively), but with a significant fraction of Al-OH (11-16% and 22-32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH + SiOH) ratio is likely smaller than the Al/(Al + Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al + Si) ratio at higher temperatures. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2014.05.017

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Language：English   Publishing type：Part of collection (book)   Publisher：MINERALOGICAL SOC AMER & GEOCHEMICAL SOC  

DOI： 10.2138/rmg.2014.78.15

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We report the crystal structures determined under ambient condition for two Zn2SiO4 polymorphs synthesized at 6.5 GPa and 1,273 K (phase III) and 8 GPa and 1,273 K (phase IV) and also compare their Si-29 MAS NMR spectroscopic characteristics with those of other Zn2SiO4 polymorphs (phases I, II and V). Electron microprobe analysis revealed that both of phases III and IV are stoichiometric like the lower-pressure polymorphs (phases I and II), contrary to previous report. The crystal structures were solved using an ab initio structure determination technique from synchrotron powder X-ray diffraction data utilizing local structural information from Si-29 MAS NMR as constraints and were further refined with the Rietveld technique. Phase III is orthorhombic (Pnma) with a = 10.2897(5), b = 6.6711(3), c = 5.0691(2) a"<<. It is isostructural with the high-temperature (Zn1.1Li0.6Si0.3)SiO4 phase and may be regarded as a 'tetrahedral olivine' type that resembles the 'octahedral olivine' structure in the (approximately hexagonally close packed) oxygen arrangement and tetrahedral Si positions, but has Zn in tetrahedral, rather than octahedral coordination. Phase IV is orthorhombic (Pbca) with a = 10.9179(4), b = 9.6728(4), c = 6.1184(2) a"<<. It also consists of tetrahedrally coordinated Zn and Si and features unique edge-shared Zn2O6 dimers. The volumes per formula under ambient condition for phases III and IV are both somewhat larger than that of the lower-pressure polymorph, phase II, suggesting that the two phases may have undergone structural changes during temperature quench and/or pressure release.

DOI： 10.1007/s00269-013-0584-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Structural characterization of a new high-pressure AlPO4 phase synthesized at 5 GPa and 1500 degrees C is reported. The phase is monoclinic (P2/a) with a = 8.7437(1) angstrom, b = 4.8584(1) angstrom, c = 10.8600(2) angstrom, beta = 90.124(1)degrees (Z = 6). P-31 MAS NMR and two-dimensional (2D) Al-27 triple-quantum (3Q) MAS NMR revealed that it contains two tetrahedral P sites of 1:2 abundance ratio, and two tetrahedral Al sites with 1:2 ratio. 2D P-31 dipolar-recoupled double-quantum (DQ) MAS NMR and Al-27 -> P-31 dipolar-based (through-space) and J coupling-based (through-bond) 3Q-heteronuclear correlation (HETCOR) experiments provided direct information on the linkages of these sites. The crystal structure was solved and refined from synchrotron powder X-ray diffraction data utilizing the information from NMR. The phase is isostructural to moganite, a rare SiO2 polymorph, and its structure can be derived from the latter via an ordered replacement of tetrahedral Si sites by Al and P. The NMR parameters of the phase were also calculated by first-principles method, which are consistent with those observed. Contrary to the other moganite phases known to date (i.e., SiO2 and PON), moganite-AlPO4 has a higher-pressure stability field than the corresponding quartz phase. This is the first moganite-type phase found in the ABX(4) system.

DOI： 10.1021/ic300167k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Si-29 MAS NMR is a well-established tool for quantitative characterization of Si-Al distribution in aluminosilicates. In framework aluminosilicates, all tetrahedrally coordinated Si/Al (T) are linked via bridging oxygens to four other Si/Al (Q(4)). Each crystallographically unique T site is commonly assumed to give at most five Si-29 NMR peaks with chemical shift spacing around 5 ppm, corresponding to five Si units each linked to nSi and (4 - n)Al (n = 0-4), abbreviated as Si(nSi) hereafter. Here we report a detailed one- and two-dimensional (2D) Si-29 NMR study on K-cymrite (KAlSi3O8 center dot H2O), which possesses a double-layered structure with all Si/Al distributed in one crystallographically unique T site (Q(4)). Contrary to general belief, more than five Si-29 MAS NMR peaks were resolved. These peaks are attributable, via 2D J-coupling mediated experiments, to Si(nSi)(n = 0-4), with two peaks each (similar to 2 ppm spacing) for n = 1-3. The latter corresponds to different permutations of the nSi(4 - n)Al over neighboring T sites of two distinct Si-O-T angles (139 and 180 degrees). This suggests for the first time that the Si-29 chemical shift varies with Si-O-Si and Si-O-Al angles differently. Si-Al exchange over neighboring T sites of unequal Si-O-T angles is another possible cause for multiple Si-29 NMR peaks.

DOI： 10.1021/jp3008859

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ASSOC MINERALOGICAL SCIENCES  

To facilitate identification of high-pressure K-cymrite (KAlSi3O8 center dot H2O) phase and its anhydrous form (kokchetavite) in natural rocks, we have synthesized both phases and have characterized them by micro-Raman and NMR spectroscopy. K-cymrite was synthesized at 5 GPa and 800 degrees C. Kokchetavite was obtained by dehydrating K-cymrite at ambient pressure and 550 degrees C. The H-1 MAS and H-1-Si-29 CP MAS NMR spectra of K-cymrite are consistent with the reported crystal structure that contains H2O molecules and has a disordered Si-Al distribution. The Raman spectra obtained under ambient conditions for K-cymrite (and kokchetavite) contain major peaks at 114.0 (109.1), 380.2 (390.0) and 832.5 (835.8) cm(-1). For K-cymrite, OH stretching vibration is also observed at 3541 cm(-1) with a shoulder at 3623 cm(-1). The Raman spectrum for kokchetavite is consistent with that previously reported for a natural sample found as inclusions in clinopyroxenes and garnets in a garnet-pyroxene rock. However, the data for K-cymrite are inconsistent with the Raman features of a previously reported "relict K-cymrite in K-feldspar" from an eclogite. Pressure- and temperature-dependencies of the Raman shifts for the strongest peak of both phases are also reported.

DOI： 10.2465/jmps.111020i

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WALTER DE GRUYTER GMBH  

The crystal chemistry of armenite, ideally BaCa2Al6Si9O30 center dot 2 H2O, from Wasenalp, Valais, Switzerland was studied. Armenite typically forms in relatively low-temperature hydrothermal veins and fissures and has small pores containing Ca cations and H2O molecules as extra-framework species. Single-crystal neutron and X-ray diffraction measurements were made on armenite from the above locality for the first time. IR powder spectroscopic measurements were made from room temperature (RT) down to 10 K. H-1 and Si-29 NMR measurements were made at RT. Attention was given to investigating the behavior of the extra-framework species and hydrogen bonding. The diffraction results show new features not observed before in published diffraction studies on armenite crystals from other localities. The neutron results also give the first static description of the protons, allowing bond distances and angles relating to the H2O molecules and H-bonds to be determined. The diffraction results indicate Al/Si order in the framework. Four crystallographically independent Ca and H2O molecule sites were refined, whereby both sites appear to have partial occupancies such that locally a Ca atom can have only a single H2O molecule bonded to it through an ion-dipole interaction. The Ca cation is further bonded to six O atoms of the framework forming a quasi cluster around it. The IR spectrum of armenite is characterized in the OH-stretching region at RT by two broad bands at roughly 3470 and 3410 cm(-1) and by a single H2O bending mode at 1654 cm(-1). At 10K four intense OH bands are located at 3479, 3454, 3401 and 3384 cm(-1) and two H2O bending modes at 1650 and 1606 cm-(1). The (29)si MAS NMR spectra show four resonances at -81.9, -83.2, -94.9 and -101.8 ppm that are assigned to crystallographically different Si sites in an ordered structure, although their relative intensities deviate somewhat from those predicted for complete Al/Si order. The H-1 MAS spectra contain a single main resonance near 5.3 ppm and a smaller one near 2.7 ppm, which can be assigned to H2O molecules bonded to Ca and a second H2O type located in a partially occupied site, respectively. Bonding for the extra-framework "Ca-oxygen-anion-H2O-molecule quasi-clusters" and also the nature of H-bonding in the microporous zeolites scolecite, wairakite and episilbite are analyzed. The average OH stretching wavenumbers shown by the IR spectra of armenite and scolecite are, for example, not far removed from that observed in liquid H2O, but greater than that of ice. What remains poorly understood in microporous silicates is how the ion-dipole interaction in quasi clusters affects H-bonding strength between the H2O molecules and the aluminosilicate framework.

DOI： 10.1524/zkri.2012.1515

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The crystal structures of two new high-pressure AlPO4 phases are reported. One phase synthesized at 6 GPa and 1523 K is triclinic (P (1) over bar) whilst the other phase synthesized at 7 GPa and 1773 K is monoclinic (P2(1)/c). P-31 MAS (magic-angle spinning) NMR suggests three tetrahedral P sites with equal abundance in both phases. Al-27 3Q MAS NMR spectra provided evidence for two octahedral sites and one five-coordinated Al site in each phase. The crystal structures were solved using an ab initio structure determination technique from synchrotron powder X-ray diffraction data utilizing the local structural information from NMR, and were further refined by the Rietveld method. Both phases contain doubly bent chains made of six edge-shared Al polyhedra (including five-coordinated Al), which are joined by PO4 tetrahedra. The P (1) over bar phase is isostructural with FeVO4 and AlVO4. The two phases differ in the packing manner of the chains. This study has demonstrated that the combined application of ab initio structure determination via X-ray powder diffraction and solid-state NMR spectroscopy is a powerful approach to the rapid solution of complex inorganic crystal structures.

DOI： 10.1107/S0108768110051050

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

A systematic study utilizing rotor-synchronized homonuclear (P-31, Al-27) and heteronuclear ({P-31}Al-27 and (Al-27)P-31) spin echo, and {Al-27}P-31 refocused INEPT experiments (employing soft pulses for selective excitation of the central transition for the quadrupolar Al-27 (I=5/2)) have been performed on AlPO4 berlinite at 30 kHz MAS to better understand the J modulation behavior involving half-integer quadrupolar nuclei in solid materials with framework structure. Analyses of the J modulation on either the Al-27 or P-31 coherence in both the {P-31}Al-27 and {Al-27}P-31 spin echo experiments, and both periods of the refocused INEPT experiment yield consistent results for the (2)J(AlP)(Al-O-P) coupling constant (ca. 25 Hz). It is noted that the coupling of each Al-27 to four P-31 spins during the first (Al-27) evolution period of the refocused INEPT, and the populations of P-31 coupled to different numbers (0-4) of Al-27 in the +/- 1/2 Zeeman states during P-31 coherence evolution, which have been neglected in previous studies, must be taken into account for proper treatment. Analysis off modulation on the spin (Al-27) coupled to spin-1/2 nuclei in general gives more accurate results. Weak long-range homonuclear (4)J(PP)(P-O-Al-O-P) coupling was also observed from the P-31 spin echo and INADEQUATE experiments. (C) 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ssnmr.2010.09.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

A new polymorph of topaz-OH (denoted as topaz-OH H) was recently discovered at higher P-T conditions than has been known thus far (denoted as topaz-OH I). High-resolution H-1, Si-29, and Al-27 nuclear magnetic resonance (NMR) and micro-Raman spectroscopy are applied to shed light on the crystal chemistry of both polymorphs. Topaz-OH I, synthesized at 7 GPa and 640 degrees C, is stoichiometric (Si/Al = 0.5) with a largely ordered local structure. Higher P-T topaz-OH I synthesized at conditions close to the polymorphic phase transition boundary, on the other hand, shows lower Si/Al ratios (0.44-0.45) and greater local structural disorder [including a small fraction (similar to 3%) of octahedral Si with a unique Si-29 chemical shift near 133 ppm]. The latter may be accounted for by the development of defects (Si/Al in normally vacant octahedral sites and vacancies in the tetrahedral sites) at higher P-T conditions. Topaz-OH II synthesized at 13.5 similar to 14 GPa and 1300 similar to 1400 degrees C similarly exhibits low Si/Al ratios (0.41-0.46). The NMR and Raman spectra for these topaz-OH II are, in general, broader and revealed a substantial fraction (33-37%) of octahedral Si with a range of Si-29 chemical shifts (-130 to -190 ppm), a small fraction (2-3%) of tetrahedral Al, and a range of (and overall shorter) hydrogen-bonding distances than topaz-OH I. Therefore, the phase transition from topaz-OH I to II is characterized by both a significant increase in the occupied octahedral/tetrahedral site ratio as well as disordering of cation distribution, which is unique from the viewpoint of crystal chemistry.

DOI： 10.2138/am.2010.3471

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

The Component-Resolved methodology was applied to H-1 spin-echo and Al-27-H-1 cross polarization (CP) MAS NMR data of aluminosilicate glasses. The method was able to resolve two components with different T2 relaxation rates, hydroxyl groups (OH) and molecular water (H2Omol), from the spin-echo data and to determine partial spectra and the relative abundances of OH and H2Omol. The algorithm resolved two to three components with different Al-27-H-1 CP dynamics from the Al-27-H-1 cross polarization data; the obtained partial NMR spectra for Al-OH are in excellent agreement with those obtained previously from the difference spectra between spectra with various contact times and confirm previous quantitative results and models for the Al-OH, Si-OH and H2Omol speciation (Malfait and Xue, 2010). (C) 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ssnmr.2010.04.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The combined results of Al-27-H-1 and H-1-Si-29-H-1 cross polarization NMR experiments for hydrous glasses (containing 0.5-2 wt% water) along the SiO2-NaAlSiO4 join confirm that the dissolution mechanism of water in aluminosilicate glasses is fundamentally the same as for Al-free systems, i.e. the dissolved water ruptures oxygen bridges and creates Si-OH and Al-OH groups, in addition to forming molecular water (H2Omol). The fraction of Al-OH increases non-linearly as the Al content increases with up to half of the OH groups as Al-OH for compositions close to NaAlSiO4. The relative abundances of the different species are controlled by the degree of Al-avoidance and the relative tendency of hydrolysis of the different types of oxygen bridges, Si-O-Si, Si-O-Al and Al-O-Al. A set of homogeneous reactions is derived to model the measured Al-OH/Si-OH speciation, and the obtained equilibrium constants are in agreement with literature data on the degree of Al-avoidance. With these equilibrium constants, the abundance of the different oxygen species, i.e. Si-O-Si, Si-O-Al, Al-O-Al, Si-OH, Al-OH and H2Omol, can be predicted for the entire range of water and Al contents. (c) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2009.10.036

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Language：English   Publisher：WILEY  

Solid-state 1H nuclear magnetic resonance (NMR) spectroscopy has developed into a versatile, high-resolution method for elucidating the detailed structures of both crystalline and amorphous materials. Here, we summarize our recent endeavors in applying this method to crystalline and glassy silicates and related inorganic materials. We first present updated correlations between 1H chemical shift and O circle dot O and H circle dot O distances of O-H circle dot O hydrogen bonds, derived from a comprehensive 1H chemical shift database containing both original high-quality fast magic angle spinning (MAS) and two-dimensional combined rotation and multiple pulse spectroscopy (CRAMPS)-MAS NMR data and literature MAS NMR data for a large number of inorganic compounds, including phosphates, silicates, (oxy)hydroxides, borates, sulfates, and carbonates. These correlations may be used to estimate hydrogen-bonding distances for inorganic oxide materials of unknown structures. We then present case studies for the application of high-resolution two-dimensional 1H CRAMPS-MAS NMR to unravel the order/disorder of proton distributions in crystalline high-pressure hydrous silicates. Finally, we summarize some of our results on the water speciation in hydrous (alumino)silicate glasses of a range of compositions obtained through comprehensive 1H MAS NMR, and 29Si-1H and 27Al-1H double-resonance NMR experiments, and analyze them in the framework of a quasi-chemical model.

DOI： 10.1111/j.1551-2916.2009.03468.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

High-resolution Si-29 and Al-27 NMR techniques have been applied to resolve the Si-Al distribution and coordination in the high-pressure CaAl4Si2O11 (CAS) phase, a potentially important mineral in subducted crustal materials in the deep mantle that has a unique hexagonal ferrite structure containing two octahedral (M1; M2) and one trigonal bipyramidal sites. The Si-29 MAS NMR spectra of the CAS phase synthesized at 20 GPa and 1400 similar to 1600 degrees C show two broad, asymmetric peaks near -92.7 and -182.7 ppm with an intensity ratio of 1:3, suggesting that 1/4 of the Si are in tetrahedral coordination and 3/4 in octahedral coordination. Therefore, the trigonal bipyramidal and M1 octahedral sites are each occupied by equal proportions of Si and AI, and the former are effectively half-occupied face-sharing tetrahedra (at least for Si). The Al-27 MAS and 3Q MAS NMR spectra contain only one unresolved peak typical of octahedral Al with a range of quadrupolar coupling constants.

DOI： 10.2138/am.2009.3348

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Through a combination of H-1 MAS NMR, H-1 -> Si-29 -> H-1 double cross-polarization (CP) MAS NMR and Al-27 -> H-1 CP MAS NMR, different OH species [SiOH, AlOH, and (Ca,Mg)OH (free OH)] have been unambiguously identified for hydrous Ca,Mg-(alumino)silicate glasses. This confirms my earlier speciation assignments made partially on the basis of H-1 chemical shift arguments. The dissoution mechanisms of water in both Al-free silicate and aluminosilicate glasses (quenched melts) are fundamentally similar. For relatively polymerized compositions, it involves dominantly the formation of TOH species (T: Si, Al) through the rupture of T-O-T linkages, in addition to molecular H2O; for more depolymerized compositions containing network-modifying cations of large field strength (e.g., Ca, Mg), free Oil species are also important.

DOI： 10.2138/am.2009.3088

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

To gain new structural insights into phase D and superhydrous B, two phases of potential mantle water reservoir, we have applied a range of one- (1D) and two-dimensional (2D) H-1 and Si-29 NMR techniques, as well as Raman spectroscopy, to samples synthesized at 24 GPa and 900 similar to 1100 degrees C. These data have revealed that phase D is characterized by disordered and varying local structures around both Si and H. The Si-29 NMR spectra of phase D contain a nearly symmetric, broad peak near -177.7 ppm, attributable to octahedral Si with local structural disorder. The high-resolution H-1 CRAMPS spectra of phase D contain a main broad peak near 12.6 ppm with shoulders near 10 and 7 ppm, suggesting a distribution of hydrogen bonding distances. For superhydrous B, our comprehensive 2D H-1 and Si-29 NMR results have clearly revealed that it contains dissimilar hydrogen (H1-H2) pairs and one tetrahedral Si site, consistent with space group Pnn2.

DOI： 10.2138/am.2008.2751

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We have taken a systematic approach utilizing advanced solid-state NMR techniques to gain new insights into the controversial issue concerning the dissolution mechanisms of water in aluminosilicate melts (glasses). A series of quenched anhydrous and hydrous (similar to 2 wt% H2O) glass samples along the diopside (Di, CaMgSi2O6) - anorthite (An, CaAl2Si2O8) join with varying An components (0, 20, 38, 60, 80, and 100 mol%) have been studied. A variety of NMR techniques, including one-dimensional (ID) H-1 and Al-27 MAS NMR, and Al-27 -> H-1 cross-polarization (CP) MAS NMR, as well as two-dimensional (M) H-1 double-quantum (DQ) MAS NMR Al-27 triple-quantum (3Q) MAS NMR, and Al-27 -> H-1 heteronuclear correlation NMR (HETCOR) and 3QMAS/HETCOR NMR, have been applied. These data revealed the presence of SiOH, free OH ((Ca,Mg)OH) and AlOH species in the hydrous glasses, with the last mostly interconnected with Si and residing in the more polymerized parts of the structure. Thus, there are no fundamental differences in water dissolution mechanisms for Al-free and Al-bearing silicate melts (glasses), both involving two competing processes: the formation of SiOH/AlOH that is accompanied by the depolymerization of the network structure, and the formation of free OH that has an opposite effect. The latter is more important for depolymerized compositions corresponding to mafic and ultramafic magmas.Aluminum is dominantly present in four coordination (Al-IV), but a small amount of five-coordinate Al (Al-V) is also observed in all the anhydrous and hydrous glasses. Furthermore, six-coordinate Al (Al-VI) is also present in most of the hydrous glasses. As Al of higher coordinations are favored by high pressure, (AlOH)-O-VI and (AlOH)-O-V may become major water species at higher pressures corresponding to those of the Earth's mantle. (c) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2008.01.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

In order to shed light on the proton distributions and order/disorder in high-pressure delta-Al(OH)(3) and delta-AlOOH phases, two-dimensional, high-resolution H-1 CRAMPS (FSLG)-MAS NMR and Al-27 3QMAS NMR spectra have been obtained. For delta-Al(OH)(3), the H-1 CRAMPS-MAS NMR revealed two peaks with an intensity ratio close to 2:1. The Al-27 MAS and 3QMAS NMR suggest a single Al site with a well-defined local structure. For delta-AlOOH, the H-1 and Al-27 NMR indicate the presence of a single H and Al site each. These results are consistent with crystal structures refined from X-ray diffraction. For comparison, 1H MAS and CRAMPS-MAS NMR spectra were also obtained for several other hydroxides/oxyhydroxides, including In(OH)(3) and InOOH that have similar structures to delta-Al(OH)(3) and delta-AlOOH, respectively. These data not only provide additional insights into the proton distributions in these important crystal structure classes but also together provide a better defined quantitative correlation between 1H chemical shift and hydrogen-bonding O center dot center dot center dot O distance.

DOI： 10.1021/jp073968r

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

dIn order to shed light on the dissolution mechanisms of water in depolymerized aluminosilicate melts/glasses, a comprehensive one(113) and two-dimensional (2D) NMR study has been carried out on hydrous Ca- and Mg-aluminosilicate glasses of a haplobasaltic composition. The applied techniques include 1D H-1 MAS NMR and Al-27 -> H-1 cross-polarization (CP) MAS NMR, and 2D H-1 NOESY and double-quantum (DQ) MAS NMR, Al-27 triple-quantum (3Q) MAS NMR and 27 -> H-1 heteronuclear correlation (HETCOR) and 3QMAS/HETCOR NMR. Ab initio calculations were also performed to place additional constraints on the 1H NMR characteristics of AlOH and Si(OH)AI groups. This study has revealed, for the first time, the presence of free OH (i.e. (Ca, Mg)OH), SiOH and AlOH species, in addition to molecular H2O, in hydrous glasses of a depolymerized alummosilicate composition. The AlOH groups are mostly associated with four-coordinate Al, but some are associated with five- and six-coordinate Al. (c) 2006 Published by Elsevier Inc.

DOI： 10.1016/j.ssnmr.2006.11.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

We have applied one-dimensional (1D) H-1 MAS NMR Al-27 -> H-1 CP MAS NMR, as well as 2D(27)Al triple-quantum (3Q) MAS NMR, Al-21 -> H-1 heteronuclear correlation (HETCOR) and high-resolution 3QMAS/HETCOR NMR techniques to KAlSi3O8 (Or), NaAlSi3O8 (Ab) and NaAlSiO4 (Ne) glasses containing 0 similar to 2 wt% H2O to shed light on the dissolution mechanisms of water in aluminosilicate melts (glasses). An Al Q(3)-OH group, characterized by H-1 chemical shifts of 1.3-1.9 ppm, was identified for all hydrous glasses. Its abundance increases with bulk Al/Si ratio. The Al-27 chemical shifts (partial derivative(Al)(i)) of this species are 64-68 ppm, larger than those of Al Q(4) by 3-6 ppm. Despite this difference, it is only through Al-27 -> H-1 HETCOR and 3QMAS/HETCOR, but not Al-27 MAS or 3QMAS NMR that the peaks are resolved. This study has demonstrated that depolymerization and formation of AlOH/SiOH is a general water dissolution mechanism for polymerized aluminosilicate melts (glasses), and HETCOR NMR experiments involving H-1 are the key to its revelation.

DOI： 10.2138/am.2006.2365

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Topaz-OH, phase egg, and delta-AIOOH are hydrous phases in the Al2O3-SiO2-H2O system that have been found to be stable at successively higher pressures up to those corresponding to the lower mantle, and thus they may be important water reservoirs in the deep mantle. We have applied H-1, Si-29, and Al-27 nuclear magnetic resonance (NMR) and Raman spectroscopy to shed new light on the structure of these phases. Si-29 and (27)AI NMR results clearly revealed that the Si-Al distribution in phase egg is partially disordered. The presence of structural disorder in topaz-OH was also confirmed. H-1 NMR and Raman data are both consistent with strong, but asymmetric hydrogen bonding in delta-AlOOH and phase egg, and a range of hydrogen bonding distances in topaz-OH. The observed structural disorder and hydrogen bonding could be responsible for the high upper temperature stability limits (1500 similar to 1700 degrees C) of phase egg and topaz-OH, and are also relevant to the incorporation mechanisms of water in nominally anhydrous stishovite.

DOI： 10.2138/am.2006.2064

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Publisher：Japan Association of Mineralogical Sciences  

We have calculated electric field gradients (EFG) of various crystals using FPLAPW method. Calculated Cq and asymmetry parameter of oxygen well reproduced experimental NMR data within 5 %, except for hydrogen containing systems. Therefore such calculations allow us to uniquely assign NMR peaks to certain sites with confidence.

DOI： 10.14824/kobutsu.2005.0.23.0

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Publisher：Japan Association of Mineralogical Sciences  

Topaz-OH (Al2SiO4(OH)2), phase egg (AlSiO3OH) and delta-AlOOH are hydrous phases in the Al2O3-SiO2-H2O system that have been found to be stable at successively higher pressures up to those of the lower mantle, and thus may be important in the siliceous sediments of subducting slab. Although the crystal structures of these phases have been determined by X-ray diffraction, this technique is insensitive to H positions and Al-Si disorder. We have applied 1H, 29Si and 27Al NMR and micro-Raman spectroscopy to gain additional insights. Our study revealed that the octahedral Al-Si distribution in phase egg is partially disordered, which is expected to have a significant effect on its physical and thermodynamic properties and stability field. In addition, these data also suggest the presence of some structural disorder in topaz-OH. Finally, our data support that hydrogen bonding is strong in phase egg and delta-AlOOH, but weak in topaz-OH.

DOI： 10.14824/kobutsu.2005.0.45.0

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DOI： 10.1016/j.gca.2004.08.025

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DOI： 10.1016/j.gca.2004.08.029

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DOI： 10.1021/jp0040751

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DOI： 10.1021/jp992108a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER VERLAG  

In order to gain insight into the correlations between Si-29, O-17 and H-1 NMR properties (chemical shift and quadrupolar coupling parameters) and local structures in silicates, ab initio self-consistent field Hartree-Fock molecular orbital calculations have been carried out on silicate clusters of various polymerizations and intertetrahedral (Si-O-Si) angles. These include Si(OH)(4) monomers (isolated as well as interacting), Si2O(OH)(6) dimers (Cz symmetry) with the Si-O-Si angle fixed at 5 degrees intervals from 120 degrees to 180 degrees, Si3O2(OH)(8) linear trimers (C-2 symmetry) with varying Si-O-Si angles, Si3O3(OH)(6) three-membered rings (D-3 and C-1 symmetries), Si4O4(OH)(8) four-membered ring (C-4 symmetry) and Si8O12(OH)(8) octamer (D-4 symmetry). The calculated Si-29, O-17 and H-1 isotropic chemical shifts (delta(i)(Si), delta(i)(O) and delta(i)(H)) for these clusters are all close to experimental NMR data for similar local structures in crystalline silicates. The calculated O-17 quadrupolar coupling constants (QCC) of the bridging oxygens (Si-O-Si) are also in good agreement with experimental data. The calculated O-17 QCC of silanols (Si-O-H) are much larger than those of the bridging oxygens, but unfortunately there are no experimental data for similar groups in well-characterized crystalline phases for comparison. There is a good correlation between delta(i)(Si) and the mean Si-O-Si angle for both Q(1) and Q(2), where Q(n) denotes Si with n other tetrahedral Si next-nearest neighbors. Both the delta(i)(O) and the O-17 electric field gradient asymmetry parameter, eta of the bridging oxygens have been found to depend strongly on the O site symmetry, in addition to the Si-O-Si angle. On the other hand, the O-17 QCC seems to be influenced little by structural parameters other than the Si-O-Si angle, and is thus expected to be the most reliable O-17 NMR parameter that can be used to decipher Si-O-Si angle distribution information. Both the O-17 QCC and the H-2 QCC of silanols decrease with decreasing length of hydrogen bond to a second O atom (Si-O-H ... O), and the delta(i)(H) increase with the same parameter.

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DOI： 10.1007/s002690050157

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

In order to understand the correlations between O-17 NMR parameters and the local structure around 0 in high-pressure silicates, we have obtained O-17 MAS and static NMR spectra on several crystalline alkali silicate and silica phases, as well as on ambient pressure glasses. Our results show that 110 NMR is capable of distinguishing nonbridging O atoms (NBO), bridging atoms (BO: [4]Si-O-[4]Si), O atoms in the [4]Si-O-[6]Si linkage, and O atoms coordinated to three [6]Si ([3]O). NBO are characterized by small quadrupolar coupling constants (e2qQ/h, approximately 2.3 MHz), but their isotropic chemical shifts (delta(i)) are very sensitive to the type of network-modifying cations. The [3]O (in stishovite), on the other hand, has by far the largest e2qQ/h value (6.5 MHz) and a larger delta(i) (109 ppm) than any BO in silicates. BO and [4]Si-O-[6]Si both have intermediate e2qQ/h values (approximately 4.5-5.7 MHz), and the delta(i) value of the latter (97 ppm in wadeite-K2Si4O9) is larger than those of the former (approximately 50-65 ppm).
We have also applied O-17 NMR to study the structure of alkali silicate glasses quenched from melts at high pressure. The O-17 NMR spectra of a K2Si4O9 glass quenched from 6 GPa and of Na2Si4O9 glasses quenched from 6 to 10 GPa are consistent with the presence of O sites in the [4]Si-O-[6]Si (and possibly also [4]Si-O-[5]Si) linkage, supporting our previous model developed from Si-29 NMR. In addition, O-17 static NMR also reveals the development of another new type of O site, possibly one that is connected with two or three [6]Si or [5]Si atoms, in the Na2Si4O9 glass quenched from 10 GPa. Thus, [6]Si and [5]Si may be largely isolated from one another below 10 GPa, whereas at higher pressure, clustering of these Si species may become significant in Na2Si4O9 melts.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER VERLAG  

Stishovite, a high-pressure SiO2 polymorph in which each Si is coordinated by six O atoms, transforms to an amorphous phase when undergoing heat treatment below the glass transition temperature at ambient pressure. We have applied Si-29 magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) to study this amorphization process. We found that the amorphous phase generated after heating stishovite for up to 3 days at around 600-degrees-C consisted exclusively of four-coordinate Si, similar to glasses quenched from melts at ambient pressure. Furthermore, our data suggest that there are subtle structural differences between the amorphous phase transformed from stishovite at 600-degrees-C and glasses quenched from melts at ambient pressure: the amorphous phase from stishovite had a smaller mean Si-O-Si angle initially, and it gradually relaxed toward the latter with increasing heating time. There was no detectable change in the stishovite structure even after about 80% of it had been converted to the amorphous phase. The mechanism of the amorphization of stishovite is discussed in light of these results.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER CRYSTALLOGRAPHIC ASSOC  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We have studied quenched high pressure phases in the CaSiO3 system by x-ray diffraction (XRD) and Si-29 MAS NMR. XRD study of the previously reported "epsilon-CaSiO3 phase" synthesized at 12 GPa and 1500-degrees-C reveals that it is actually a mixture of beta-Ca2SiO4 (larnite) and a previously unknown CaSi2O5 phase. This result is supported by the Si-29 NMR spectra. Furthermore, both the XRD and the NMR data suggest that the CaSi2O5 phase may have a titanite (CaTiSiO5) structure in which Ti is replaced by an octahedral Si. Samples quenched from 15 GPa and 1500-degrees-C consist mostly of an amorphous phase, but a small amount of CaSiO3-perovskite was identified by both XRD and NMR. The Si-29 NMR spectrum of the amorphous phase suggests that its local structure is similar to that of a glass quenched from melt at 1 bar.

DOI： 10.1029/91GL00463

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

The Si-29 and Na-23 NMR, Raman, and infrared spectra of glasses quenched from liquids at pressures up to 12 GPa for three alkali silicate compositions (Na2Si2O5, Na2Si4O9, K2Si4O9) and silica (SiO2) reveal systematic changes in the melt structure with pressure. The most novel change is the occurrence of [5]Si and [6]Si species at high pressures identified by peaks in the Si-29 MAS NMR spectra of the alkali silicate glasses. The abundances of both [5]Si and [6]Si increase with pressure. At a given pressure there are more such species in the Na2Si4O9 composition than in Na2Si2O5 composition. These species are not observed in a SiO2 glass quenched at 6 GPa. The occurrence of these highly coordinated Si species is consistent with changes in the Raman and infrared spectra of the alkali silicate glasses, although the peak assignments in these spectra are not unique. The change in Si coordination with pressure and composition in these compositions can be accounted for by a model in which [5]Si and [6]Si form at the expense of nonbridging O atoms. This model may be generalized to all partially depolymerized melts. Changes in the tetrahedral structure with increasing pressure include Q speciation disproportionation, reduction of mean Si-O-Si angle, and development of new [4]Si species that share O with [5]Si or [6]Si. The observed structural changes have implications for the physical and thermodynamic properties of silicate melts. [5]Si has been previously envisaged as a transient state for the viscous flow and diffusion processes in silicate melts. The occurrence of [5]Si in the high pressure glasses suggests that [5]Si represents a local energy minimum and its stabilization may partly account for the enhancement of these dynamic processes. Increased configurational entropy as a result of greater distribution of Si coordinations and Q species at high pressures could also contribute to the reduced melt viscosity.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

DOI： 10.1126/science.245.4921.962

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

To help identification of K-cymrite (KAlSi3O8*H2O) and its anhydrous form (kokchetavite) in UHP metamorphic rocks, K-cymrite and kokchetavite are studied by Raman spectroscopy. K-cymrite is produced at 5 GPa and 800 C. Kokchetavite is made by dehydration of K-cymrite heating up to 800 C. In-situ high pressure Raman spectra of two phases are obtained using diamond anvil cell. Raman shifts of the main peak for K-cymrite and kokchetavite are 380 and 390 cm-1, respectively. Our result reveals that the previously reported K-cymrite from China (Zhang et al., AM, 2008) would be kokchetavite rather than K-cymrite. Pressure dependences of Raman shifts for main peaks for K-cymrite and kokchetavite are 4.9 and 5.6 cm-1/GPa, respectively.

DOI： 10.14824/jakoka.2011.0.54.0

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Language：English   Publisher：Japan Association of Mineralogical Sciences  

We have discovered a new polymorph of topaz-OH (ideal formula: Al2SiO4(OH)2) (denoted as topaz-OH II) that occurs at higher P-T conditions (13-14 GPa, 1300-1500°C) than that known thus far (denoted as topaz-OH I). The phase transition boundary has been investigated in-situ at high P-T by synchrotron X-ray diffraction, and their crystal structures characterized by powder X-ray diffraction, multi-nuclear NMR and micro-Raman spectroscopy. The crystal structure of topaz-OH II bears some similarity with those of topaz-OH I and diaspore (AlOOH), having partially occupied double edge-shared octahedral chains, and 2x1 tunnels containing partially occupied tetrahedral and octahedral sites. The phase transition from topaz-OH I to II is isochemical, and is characterized by both significant increase in the occupied octahedral/tetrahedral site ratio and disordering of cation distribution, which is rather unique from a crystal chemical point of view.

DOI： 10.14824/jakoka.2010.0.70.0

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

High-pressure quench experiments of AlPO₄ revealed two new polymorphs at 6-7 GPa. "I" stabilized at 1000°C, and "II" stabilized at 1500°C. ³¹P MAS NMR revealed three tetrahedral P sites of equal abundances in each phase. ²⁷Al MQ MAS NMR unveiled two octahedral and one penta-coordinated Al sites for each phase. We solved the crystal structures using the "FOX" program (direct-space searching method), using the information from NMR to constrain the number and types of polyhedra. The space group of I was P-1, whereas, that of II was P2₁/c. The length of a- and c-axes are similar, however, that of b-axis of II was about twice of that of I. The densities of two phases are almost the same, and are 28% larger than that of quartz phase. Both phases contain short chains made of edge-shared six Al-polyhedra which are interconnected by PO₄ tetrahedra to form 3D network.

DOI： 10.14824/jakoka.2009.0.127.0

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Language：English  

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

In recent years we have made much progress in unraveling the water dissolution mechanisms in hydrous (alumino)silicate melts/glasses through the application of advanced solid-state NMR techniques. A range of compositions, including depolymerized Al-free silicate (e.g. CaO-MgO-SiO2), nominally fully polymerized aluminosilicate (SiO2-NaAlO4 join) and partially depolymerized aluminosilicate (CaMgSiO6 (diopside)-CaAl2Si2O8 (anorthite) join), have been investigated. Several types of hydroxyl species, including Si-OH, Al-OH and free OH (e.g. Mg-OH) have been revealed, in addition to molecular H2O; their relative abundances have been found to strongly depend on composition, and can be accounted for by a set of homogeneous reactions among oxygen species in a quasi-chemical model.

DOI： 10.14824/jakoka.2009.0.128.0

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Language：Japanese   Publisher：The Geochemical Society of Japan  

Knowledge of the atomic structures of Earth's materials is indispensible for the understanding/modeling of macroscopic geochemical processes. Solid-state NMR spectroscopy offers a rich variety of advanced multi-nuclear, multi-dimensional techniques that can provide not only quantitative information about local structures around different elements (isotopes), but also direct information concerning atomic connectivities. Recently, we have applied some of these techniques to unravel the structures of (1) high-pressure hydrous minerals in the MgO-SiO₂-H₂O and Al₂O₃-SiO₂-H₂O systems (e.g. phase egg, δ-AlOOH, phase D, superhydrous B), which represent potential water reservoirs in the Earth's mantle, and (2) hydrous (alumino) silicate glasses (quenched melts), which serve as analogs for natural magmas. For the hydrous minerals, the states of Si-Al and Si-Mg order/disorder among octahedral sites and hydrogen distribution and hydrogen-bonding distances were clearly revealed. Such information would have been difficult to obtain by any other single technique. For the hydrous aluminosilicate melts, advanced NMR techniques provided the key information needed to end a long-standing controversy concerning the water dissolution mechanisms. Some of these results are summarized here to demonstrate the usefulness and wonder of advanced solid-state NMR spectroscopy.

DOI： 10.14934/chikyukagaku.42.133

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Language：English   Publisher：Japan Association of Mineralogical Sciences  

We have applied one-dimensional (1D) 1H and 29Si MAS NMR and 1H-29Si cross-polarization (CP) MAS NMR, and 2D 1H NOESY, high-resolution 1H CRAMPS (FSLG)-MAS NMR, 1H double-quantum filtered (DQF) single-quantum (1Q) -1Q correlation MAS NMR and 1H-29Si heteronuclear correlation (HETCOR) NMR techniques to gain new insights into the structure of two phases of potential mantle water reservoir, phase D and superhydrous B. Two samples containing both phases have been synthesized from a mixture of Mg(OH)2 and SiO2 at 24 GPa and 900-1100C. For phase D, the 29Si NMR spectra contain a nearly symmetric, broad peak near -177.7 ppm, attributable to octahedral Si with a disordered local structure. The high-resolution 1H CRAMPS spectra contain a main peak near 12.6 ppm with two shoulders near 10 and 7 ppm, suggesting a disordered proton distribution, mostly with shorter hydrogen bonds than previously suggested. For superhydrous B, our 2D NMR data have clearly revealed that it contains dissimilar proton (H1-H2) pairs and one tetrahedral Si site, consistent with space group Pnn2.

DOI： 10.14824/jakoka.2007.0.130.0

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Language：Japanese   Publisher：The Ceramic Society of Japan  

In order to shed light on the proton distributions and order/disorder in high-pressure delta-Al(OH)3 and delta-AlOOH and isostructural In(OH)3 and InOOH phases, high-resolution 1H CRAMPS (FSLG)-MAS NMR and Raman spectroscopy have been applied. The 1H CRAMPS-MAS NMR revealed two peaks each for delta-Al(OH)3 and In(OH)3, and one each for delta-AlOOH and InOOH. These results are consistent with crystal structures refined from X-ray and/or neutron diffraction. The Raman spectra are also in general agreement with the NMR results.

DOI： 10.14853/pcersj.2007f.0.118.0

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DOI： 10.14862/geochemproc.54.0.211.0

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DOI： 10.1016/j.gca.2004.08.016

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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DOI： 10.1016/S0031-9201(97)00120-9

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Event date： 2022.9.17 - 2022.9.19

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