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Jonathan F Stebbins - One of the best experts on this subject based on the ideXlab platform.
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Cation order/disorder behavior and crystal chemistry of pyrope-grossular garnets: An 17O 3QMAS and 27Al MAS NMR spectroscopic study
American Mineralogist, 2015Co-Authors: Kimberly E Kelsey, Jonathan F Stebbins, Linshu Du, Jed L Mosenfelder, Paul D Asimow, Charles A GeigerAbstract:The thermodynamic mixing properties of the pyrope-grossular solid solution show large deviations from ideality, which could be partly related to Ca-Mg order/disorder. In this study, synthetic pyrope-grossular garnets with X_(Mg) = 1.00, 0.91, 0.75, 0.50, 0.24, 0.10, and 0.00 are observed using ^(17)O 3QMAS, ^(27)Al MAS, and ^(29)Si MAS NMR to examine Ca-Mg order/disorder behavior and crystal chemical variations. The ^(17)O 3QMAS NMR spectra show four distinct resonances, assigned to four different local oxygen coordination environments; two resemble end-member garnets (oxygen bonded to two Mg or two Ca) and two are intermediate (oxygen bonded to one Ca and one Mg), indicating that there are two distinct bond distances for the Mg-O and/or Ca-O bonds through the entire solid solution. Noticeable changes in the NMR peak position for two of the oxygen sites suggest that as X_(Mg) increases, the longer Ca-O bond shortens. The relative areas for the different oxygen sites are close to those predicted using a model of random Ca/Mg mixing. The maximum allowed reduction in configurational entropy from first neighbor Ca-Mg ordering is insignificant relative to other configurational entropy reductions and excess vibrational entropy. These conclusions are not inconsistent with published theoretical calculations suggesting some Ca-Mg ordering that involves correlations beyond the first neighbor, as suggested by published theoretical calculations. Even at 18.8 Tesla, the ^(27)Al MAS NMR spectra do not resolve different local Al sites with varying combinations of X cation neighbors. The ^(29)Si MAS NMR spectra have resonance broadening, probably caused by the addition of 0.15 wt% Fe_2O_3 in the synthetic samples, and are consistent with published results suggesting a small degree of Ca-Mg ordering that is not reflected in the ^(17)O NMR spectra.
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Non-bridging oxygen and high-coordinated aluminum in metaluminous and peraluminous calcium and potassium aluminosilicate glasses: High-resolution 17O and 27Al MAS NMR results
American Mineralogist, 2011Co-Authors: Linda M. Thompson, Jonathan F StebbinsAbstract:Change in configuration and structure with composition are important components of thermodynamic and transport properties of most aluminosilicate melts, but the complex interactions, particularly in metaluminous and peraluminous compositions, are not yet well understood. In this paper, we present high-resolution 27 Al and 17 O MAS and 3QMAS NMR data on several calcium and potassium aluminosilicate glasses prepared at several SiO 2 isopleths, ranging from peralkaline to peraluminous compositions. In all calcium aluminosilicate glasses, the V Al content increases with increasing Al content, while the NBO content decreases (in one series, below the limit of detection), consistent with other recent NMR studies of calcium aluminosilicate glasses. An increase in V Al content per total Al is also observed as the glass approaches the calcia-silica binary. In the potassium aluminosilicate glasses, NBO is directly quantified for the first time in metaluminous and peraluminous compositions; V Al is below the detection limit. We discuss possible mechanisms for the incorporation of alumina into the melt structure and show how changes in the V Al content as a function of composition may be used to eliminate mechanisms that do not fit the observed data. We also explore reactions, which show the difficulty of explaining the NBO present on the metaluminous join with only the observed V Al, implying the necessity of multiple reactions producing NBO in such compositions.
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Quench rate and temperature effects on boron coordination in aluminoborosilicate melts
Journal of Non-crystalline Solids, 2010Co-Authors: Jingshi Wu, Jonathan F StebbinsAbstract:Abstract The effect of temperature on the structure of aluminoborosilicate liquids has been studied by 11 B MAS NMR, 11 B 3QMAS NMR, 23 Na and 27 Al MAS NMR spectroscopies using glass samples prepared with different cooling rates and thus different fictive temperatures. The abundance of BO 3 group and non-bridging oxygen (NBO) increases with increasing fictive temperature, indicating that the reaction BO 4 ↔ BO 3 + NBO shifts to the right with increasing temperature. The observed temperature dependence of BO 4 species abundance allows us to estimate the ∆ H of this reaction to be 24 to 50 kJ mol −1 in different glass compositions, and closely related with the amount of NBOs in the glass. Configurational heat capacities have been measured by differential scanning calorimetry (DSC). We found that the redistribution of boron species (BO 4 /BO 3 ) contributes a varying range of configurational heat capacity, from 7% to 30%, with different glass compositions. 11 B 3QMAS NMR indicates two different BO 3 sites, the populations of which are also affected by fictive temperature. The exchange between two different BO 3 sites should also contribute to configurational heat capacity.
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Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results
Geochimica et Cosmochimica Acta, 2009Co-Authors: Kimberly E Kelsey, Jonathan F Stebbins, Jed L Mosenfelder, David M. Singer, Gordon E. Brown, Paul D AsimowAbstract:We examined aluminosilicate glasses containing a variety of network modifying to intermediate cations (Li, La, Sc, and Fe), quenched from melts at 1 atm to 8 GPa, to further investigate the role of cation field strength in Al coordination changes and densification. ^(27)Al Nuclear Magnetic Resonance Spectroscopy (NMR) reveals that the mean Al coordination increases with increasing pressure in the Li-containing glasses, which can be explained by a linear dependence of fractional change in Al coordination number on cation field strengths in similar K-, Na-, and Ca-containing aluminosilicate glasses (K < Na < Li < Ca). Measured recovered densities follow a similar linear trend. In contrast, the La-containing glasses have significantly lower mean Al coordination numbers at given pressures than the cation field strength of La and glass density would predict. La L_3 X-ray absorption fine structure (XAFS) spectroscopy results indicate a significant increase with pressure in average La–O bond distances, suggesting that La and Al may be “competing” for higher coordinated sites and hence that both play a significant role in the densification of these glasses, especially in the lower pressure range. However, in Na aluminosilicate glasses with small amounts of Sc, ^(45)Sc NMR reveals only modest Sc coordination changes, which do not seem to significantly affect the mean Al coordination values. For a Li aluminosilicate glass, ^(17)O MAS and multiple quantum magic angle spinning (3QMAS) NMR data are consistent with generation of more highly coordinated Al at the expense of non-bridging oxygen (NBO), whereas La aluminosilicate glasses have roughly constant O environments, even up to 8 GPa. Finally, we demonstrate that useful ^(23)Na and ^(27)Al MAS NMR spectra can be collected for Ca–Na aluminosilicate glasses containing up to 5 wt.% Fe oxide. We discuss the types of structural changes that may accompany density increases with pressure and how these structural changes are affected by the presence of different cations.
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effects of the degree of polymerization on the structure of sodium silicate and aluminosilicate glasses and melts an 17o NMR study
Geochimica et Cosmochimica Acta, 2009Co-Authors: Jonathan F StebbinsAbstract:Abstract Revealing the atomic structure and disorder in oxide glasses, including sodium silicates and aluminosilicates, with varying degrees of polymerization, is a challenging problem in high-temperature geochemistry as well as glass science. Here, we report 17 O MAS and 3QMAS NMR spectra for binary sodium silicate and ternary sodium aluminosilicate glasses with varying degrees of polymerization (Na 2 O/SiO 2 ratio and Na 2 O/Al 2 O 3 ratio), revealing in detail the extent of disorder (network connectivity and topological disorder) and variations of NMR parameters with the glass composition. In binary sodium silicate glasses [Na 2 O- k (SiO 2 )], the fraction of non-bridging oxygens (NBOs, Na–O–Si) increases with the Na 2 O/SiO 2 ratio ( k ), as predicted from the composition. The 17 O isotropic chemical shifts ( 17 O δ iso ) for both bridging oxygen (BO) and NBO increase by about 10–15 ppm with the SiO 2 content (for k = 1–3). The quadrupolar coupling products of BOs and NBOs also increase with the SiO 2 content. These trends suggest that both NBOs and BOs strongly interact with Na; therefore, the Na distributions around BOs and NBOs are likely to be relatively homogenous for the glass compositions studied here, placing some qualitative limits on the extent of segregation of alkali channels from silica-enriched regions as suggested by modified random-network models. The peak width (in the isotropic dimension) and thus bond angle and length distributions of Si–O–Si and Na–O–Si increase with the SiO 2 content, indicating an increase in the topological disorder with the degree of polymerization. In the ternary aluminosilicate glasses [Na 2 O] x [Al 2 O 3 ] 1− x SiO 2 , the NBO fraction decreases while the Al–O–Si and Al–O–Al fractions apparently increase with increasing Al 2 O 3 content. The variation of oxygen cluster populations suggests that deviation from “Al avoidance” is more apparent near the charge-balanced join (Na/Al = 1). The Si–O–Si fraction, which is closely related to the activity coefficient of silica, would decrease with increasing Al 2 O 3 content at a constant mole fraction of SiO 2 . Therefore, the activity of silica may decrease from depolymerized binary silicates to fully polymerized sodium aluminosilicate glasses at a constant mole fraction of SiO 2 .
Maria Cristina Menziani - One of the best experts on this subject based on the ideXlab platform.
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unambiguous description of the oxygen environment in multicomponent aluminosilicate glasses from 17o solid state NMR computational spectroscopy
Journal of Physical Chemistry C, 2012Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Maria Cristina MenzianiAbstract:Classical molecular dynamics simulations, density functional theory calculations, and spin-effective Hamiltonians have been used to simulate the 17O MAS and 3QMAS NMR spectra of Ca–Na silicate and aluminosilicate glasses and melts employed as simplified models for basaltic, andesitic, and rhyolitic magmas. The direct comparison of the theoretical NMR spectra of molecular dynamics derived structural models with the experimental counterparts available in the literature has allowed the investigation of the nature of nonframework cation mixing and the extent of intermixing among framework units in Na–Ca aluminosilicate glasses. In particular, in agreement with previous experimental evidence, the results show a nonrandom distribution of the network-modifying Ca and Na in soda-lime glasses with the prevalence of dissimilar Na–Ca pairs around nonbridging oxygens. The oxygen sites are not completely resolved in the MAS spectra of the aluminosilicate glasses. On the contrary, in the 17O 3QMAS spectra the multiple ...
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First-principles simulations of the ^27Al and ^17O solid-state NMR spectra of the CaAl_2Si_3O_10 glass
Theoretical Chemistry Accounts, 2012Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Gianluca Malavasi, Maria Cristina MenzianiAbstract:The local and medium-range structure of the 20CaO·20Al_2O_3·60SiO_2 glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the ^27Al and ^17O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.
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First-principles simulations of the 27Al and 17O solid-state NMR spectra of the CaAl2Si3O10 glass
Theoretical Chemistry Accounts, 2012Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Gianluca Malavasi, Maria Cristina MenzianiAbstract:The local and medium-range structure of the 20CaO·20Al2O3·60SiO2 glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the 27Al and 17O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.
Bjorn O Mysen - One of the best experts on this subject based on the ideXlab platform.
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Effect of Network Polymerization on the Pressure-Induced Structural Changes in Sodium Aluminosilicate Glasses and Melts: 27Al and 17O Solid-State NMR Study
Journal of Physical Chemistry C, 2011Co-Authors: Yoo Soo Yi, George D Cody, Kenji Mibe, Bjorn O MysenAbstract:Probing the pressure-induced structural changes and the extent of disorder in aluminosilicate glasses and melts at high pressure remains a challenge in modern physical and chemical sciences. With an aim of establishing a systematic relationship between pressure, composition, and glass structures, we report 27Al and 17O 3QMAS NMR spectra for sodium aluminosilicate glasses [Na2O:Al2O3:SiO2 = 1.5:0.5:2n with n = 1 (NAS150520, XSiO2 = 0.5), 2 (NAS150540, XSiO2 = 0.67), and 3 (NAS150560, XSiO2 = 0.75)], quenched from melts at pressures up to 8 GPa. We also explore the stability of the [4]Al–O–[4]Al cluster in the highly depolymerized, NAS150520, glass at high pressure. For given glass composition, the [5,6]Al peak intensity increases with increasing pressure. The population of [5,6]Al increases linearly with XSiO2 from NAS150520 (XSiO2 = 0.5) to NAS150560 glass (XSiO2 = 0.75) at both 6 and 8 GPa. The [5,6]Al/XSiO2 ratio also tends to increase with pressure, indicating a possible relationship between [5,6]Al fr...
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oxygen 17 nuclear magnetic resonance study of the structure of mixed cation calcium sodium silicate glasses at high pressure implications for molecular link to element partitioning between silicate liquids and crystals
Journal of Physical Chemistry B, 2008Co-Authors: George D Cody, Bjorn O MysenAbstract:The structure of silicate glasses and the corresponding liquids at high pressure and their structure−property relations remain difficult questions in modern physical chemistry, geochemistry, and condensed matter physics. Here we report high- resolution solid-state O-17 3QMAS NMR spectra for mixed cation Ca−Na silicate glasses quenched from melts at high pressure up to 8 GPa. The spectra provide the experimental evidence for the varying pressure-dependence in two different types of nonbridging oxygen (NBO) environments (i.e., Na−O−Si and mixed {Ca,Na}−O−Si) in the single glass composition. The percentage of NBO drops significantly with increasing pressure and is a complex function of melt composition, including cation field strength of network modifying cations. A decrease in NBO fraction with pressure is negatively correlated with the element partitioning coefficient between crystals and liquids at high pressure.
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The effect of Na/Si on the structure of sodium silicate and aluminosilicate glasses quenched from melts at high pressure : A multi-nuclear (Al-27, Na-23, O-17) 1D and 2D solid-state NMR study
Chemical Geology, 2006Co-Authors: George D Cody, Bjorn O MysenAbstract:Abstract We report multi-nuclear (Na-23 and O-17) solid-state NMR [MAS and triple quantum (3Q) MAS] spectra for sodium tetrasilicate glasses (NS4) quenched from melts at high pressure up to 8 GPa. The results show clear evidence for the pressure-induced structural changes in the glasses, forming oxygen linking [4] Si and [5,6] Si ( [4] Si–O– [5,6] Si) with increasing pressure. Whereas the general trend in the effect of pressure is consistent with that of sodium trisilicate glasses (NS3), detailed pressure-induced structural changes for NS4 are largely different from NS3. These differences include the larger fraction of [4] Si–O– [5,6] Si and smaller fraction of Na–O– [5,6] Si for NS4 than NS3 at isobaric conditions. Topological disorder due to Si–O bond length distribution in [4] Si–O– [4] Si is also larger for more polymerized NS4 than that for NS3, demonstrating the complexity in structural rearrangement with pressure in silicate glasses and melts with composition at elevated pressure. Na-23 MAS NMR spectra at 14.1 T for the NS4 and aluminosilicate glasses (albite composition) reveal distinct differences in Na environments within sodium silicate and aluminosilicate glasses at high pressure. Variation of isotropic chemical shift with pressure for NS4, though minor, may suggest increasing Na–O distance with pressure, possibly due to a slight increase in Na coordination at high pressure. On the other hand, Na-23 isotropic chemical shift for albite composition glass increases with increasing pressure, implying the decrease in average Na–O distance and thus free volume for non-framework cations with pressure. Higher magnetic field, coupled with 2D Al-27 3QMAS NMR, improves the resolution of Al sites for aluminosilicate glasses at high pressure and may suggest two [5] Al sites in partially polymerized aluminosilicate glasses (Na 2 O/Al 2 O 3 /SiO 2 = 15:5:60) quenched from melts at 8 GPa. The current results, together with our previous results, imply that the pressure-induced structural changes and the corresponding changes in properties in silicate melts and glasses are complex function of composition.
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Structure and the extent of disorder in quaternary (Ca-Mg and Ca-Na) aluminosilicate glasses and melts
American Mineralogist, 2005Co-Authors: George D Cody, Bjorn O MysenAbstract:The structure of multi-component silicate melts and glasses (e.g., Ca-Mg and Ca-Na aluminosilicates) can provide insight into the properties of natural silicate melts and has implications for relevant magmatic processes. In spite of its importance, the atomic and molecular structure of most multi-components (e.g., quaternary) melts and glasses has not been fully described, primarily because of insufficient resolution obtained with conventional spectroscopic and scattering methods; the information obtained by these methods is compromised by severe inhomogeneous peak broadening due to structural complexity. Here we report the first 1 7 O and 2 7 Al 3QMAS NMR spectra for quaternary, Ca-Mg and Ca-Na peralkaline aluminosilicate glasses (i.e., M/Al > 1, M is one monovalent or one-half a divalent cation). These data reveal new details into the molecular structure of multi-component aluminosilicate melts, which include the presence of a substantial fraction of V Al in the Ca-Mg aluminosilicate glasses and I V Al-O- I V Al in both glasses at 1 atm. Traditional models of glass structure do not support the presence of such species given these high-silica, peralkaline compositions. These results suggest that Al avoidance is violated in the multi-component peralkaline aluminosilicate glasses, and that the presence of Mg 2 + in the melts increases the extent of disorder in the melts (compared with Ca 2 + and Na + ). These factors lead to an increase in configurational entropy and the activity coefficients of the oxides, and may provide an explanation for the decrease in viscosity of these complex melts.
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the application of 17o and 27al solid state 3QMAS NMR to structures of non crystalline silicates at high pressure
Advances in High-Pressure Technology for Geophysical Applications, 2005Co-Authors: George D Cody, Bjorn O MysenAbstract:Abstract The recent development in two-dimensional solid-state triple quantum (3Q) magic angle spinning (MAS) NMR offers much improved resolution compared with conventional one-dimensional MAS NMR, allowing the structural details of amorphous silicates to be revealed. Since the first experimental application of 3QMAS NMR to the silicate glasses quenched from melts at high pressure in a multi-anvil apparatus [Lee, S. K., Fei, Y., Cody, G. D., Mysen, B. O., 2003a. Geophys. Res. Lett. 30, 1845], there has been continued progress in the understanding of the structures of silicate melts at high pressure. Here, we present the recent progress and insights made by O and 27 Al 3QMAS NMR spectra of silicate glasses quenched from melts at pressures up to 10 GPa in a multi-anvil apparatus, revealing new details of melt structures at high pressure . The atomic structure of sodium silicate and aluminosilicate glasses at high pressure is significantly different from that at ambient pressure. There is evidence of extensive cation ordering among highly coordinated network polyhedra, such as [5,6] Al and [5,6] Si, that affect corresponding thermodynamic and transport properties. New oxygen sites are observed at high pressure in a series of silicate glasses with varying degree of polymerization, e.g. [5,6] Al–O– [4] Si, [5,6] Si–O– [4] Si, and Na–O– [5,6] Si. The fractions of these clusters tend to increase with pressure with corresponding reduction of non-bridging oxygen (Na–O– [4] Si), thus increasing the net degree of polymerization. The fraction of [5,6] Al in aluminosilicate glasses increases with pressure, consistent with previous studies, but decreases with increasing degree of polymerization of melts from depolymerized to fully polymerized melts at an isobaric condition. The bond angle and length distribution, as well as the range in distortion of framework units increase with increasing pressure, which increases the topological entropy. These results shed light on a new opportunity for studying structures of silicate glasses and melts at high pressure and help to provide microscopic constraints for the melt properties in the Earth's interior .
Banghao Chen - One of the best experts on this subject based on the ideXlab platform.
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Surface alumina species on modified titanium dioxide: A solid-state (27)Al MAS and 3QMAS NMR investigation of catalyst supports.
Solid state nuclear magnetic resonance, 2010Co-Authors: Edward W Hagaman, Jian Jiao, Banghao Chen, Zhen MaAbstract:(27)Al MAS and 3QMAS NMR have been used to study Al(2)O(3)/TiO(2) catalyst supports synthesized via excess-solution impregnation and surface sol-gel methods. Temperature and alumina loading level strongly affect chemical states of aluminum oxide species observed. Surface cations, Al(H2O)6(3+), a surface alumina monolayer, and disordered transitional aluminas (multilayers) and alpha-alumina, coexist on the TiO(2) surface. Chemical shift and quadrupole coupling constants are reported for the major species identified in 3QMAS experiments. Gold particle catalysts prepared from supports calcined at 500 degrees C have optimum catalytic activity in CO oxidation, and smallest gold particle size for supports, which show maximum monolayer type octahedral alumina on the titania surface.
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surface alumina species on modified titanium dioxide a solid state 27al mas and 3QMAS NMR investigation of catalyst supports
Solid State Nuclear Magnetic Resonance, 2010Co-Authors: Edward W Hagaman, Jian Jiao, Banghao ChenAbstract:Abstract 27Al MAS and 3QMAS NMR have been used to study Al2O3/TiO2 catalyst supports synthesized via excess-solution impregnation and surface sol–gel methods. Temperature and alumina loading level strongly affect chemical states of aluminum oxide species observed. Surface cations, Al ( H 2 O ) 6 3 + , a surface alumina monolayer, and disordered transitional aluminas (multilayers) and α-alumina, coexist on the TiO2 surface. Chemical shift and quadrupole coupling constants are reported for the major species identified in 3QMAS experiments. Gold particle catalysts prepared from supports calcined at 500 °C have optimum catalytic activity in CO oxidation, and smallest gold particle size for supports, which show maximum monolayer type octahedral alumina on the titania surface.
Alfonso Pedone - One of the best experts on this subject based on the ideXlab platform.
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unambiguous description of the oxygen environment in multicomponent aluminosilicate glasses from 17o solid state NMR computational spectroscopy
Journal of Physical Chemistry C, 2012Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Maria Cristina MenzianiAbstract:Classical molecular dynamics simulations, density functional theory calculations, and spin-effective Hamiltonians have been used to simulate the 17O MAS and 3QMAS NMR spectra of Ca–Na silicate and aluminosilicate glasses and melts employed as simplified models for basaltic, andesitic, and rhyolitic magmas. The direct comparison of the theoretical NMR spectra of molecular dynamics derived structural models with the experimental counterparts available in the literature has allowed the investigation of the nature of nonframework cation mixing and the extent of intermixing among framework units in Na–Ca aluminosilicate glasses. In particular, in agreement with previous experimental evidence, the results show a nonrandom distribution of the network-modifying Ca and Na in soda-lime glasses with the prevalence of dissimilar Na–Ca pairs around nonbridging oxygens. The oxygen sites are not completely resolved in the MAS spectra of the aluminosilicate glasses. On the contrary, in the 17O 3QMAS spectra the multiple ...
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First-principles simulations of the ^27Al and ^17O solid-state NMR spectra of the CaAl_2Si_3O_10 glass
Theoretical Chemistry Accounts, 2012Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Gianluca Malavasi, Maria Cristina MenzianiAbstract:The local and medium-range structure of the 20CaO·20Al_2O_3·60SiO_2 glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the ^27Al and ^17O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.
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First-principles simulations of the 27Al and 17O solid-state NMR spectra of the CaAl2Si3O10 glass
Theoretical Chemistry Accounts, 2012Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Gianluca Malavasi, Maria Cristina MenzianiAbstract:The local and medium-range structure of the 20CaO·20Al2O3·60SiO2 glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the 27Al and 17O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.
