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1.
Polarized infrared (IR) spectroscopy of olivine crystals from Zabargad, Red Sea shows the existence of four pleochroic absorption bands at 3,590, 3,570, 3,520 and 3,230 cm?1, and of one non pleochroic band at 3,400 cm?1. The bands are assigned to OH stretching frequencies. Transmission electron microscopy (TEM) shows no oriented intergrowths in this olivine; it is concluded that OH is structural. On the basis of the pleochroic scheme of the absorption spectra it is proposed that [□O(OH)3] and [□O2(OH)2] tetrahedra occur as structural elements, assuming that the vacancies are on Si sites. If M2 site vacancies were assumed [SiO3(OH)] and [SiO2(OH)2] tetrahedra occur as structural elements.  相似文献   

2.
Infrared absorption spectra (400–4000 cm?1) were measured on dehydrated and partially dehydrated powder of the zeolite harmotome Ba2[(AlO2)4(SiO2)12]·12H2O. Whereas the disappearance of the bending mode at ～1640 cm?1 proved the absence of water molecules after dehydration, the O-H stretching mode at 3200 cm?1 showed the presence of hydroxyl groups. The vibrational modes of the framework are only slightly influenced by dehydration.  相似文献   

3.
Far-infrared, mid-IR, and Raman powder spectra were measured on six phases (bromellite, chrysoberyl, phenakite, bertrandite, beryl, and euclase) in the system BeO-Al2O3-SiO2-H2O. A single-crystal absorption spectrum of IR fundamentals in beryl is also presented, which more closely resembles the powder absorption spectrum than it does absorption spectra calculated from single-crystal reflection data. Assignments of the SiO4 and BeO4 internal vibrations are made in accordance with each mineral's symmetry and composition and by comparison to structural analogs. Heat capacities C v calculated for these partial band assignments agree with C v derived from experimental C p for all six phases, provided that Kieffer's (1979c) model is slightly modified to correctly enumerate both Si-O and Be-O stretching modes in the high frequency region (>750 cm?1). Si-O stretching bands were found to out-number Be-O stretching modes in the high-energy region of the vibrational spectra with two exceptions: (1) For those phases containing oxygen ions not coordinated to silicon, vibrations occurring at v>1,080 cm?1 that are attributable to Be-O (H) stretching must be treated separately in the model in order to calculate C v accurately. (2) Minerals consisting entirely of interlocking Si and Be tetrahedra (i.e., phases without Al or OH) can be modeled by one optic continuum representing all optical modes. These results, along with the occurrence of very low energy lattice vibrations for Be-silicates within Al, suggests that although Be-O bonds are generally weaker than neighboring Si-O bonds, Be mimics the network-forming characteristic of Si to a limited extent.  相似文献   

4.
Natural samples of K-feldspar representing various states of Al, Si order were characterised using X-ray methods, transmission electron microscopy, and Fourier transform infrared spectroscopy. Line profiles of infrared absorption bands were observed to show strong correlation with the degree of Al, Si order present. In particular, the absorption frequencies of the 540 cm?1 and 640 cm?1 bands were seen to vary by ca. 10 cm?1 between sanidine and microcline, with modulated samples respresenting intermediate behaviour. Linewidths of these modes also decrease by ca. 50% in this series. The experimental results are discussed within the framework of Hard Mode Infrared Spectroscopy (HMIS), and it is shown that the absorption frequencies vary with the short range order parameter τ = (4t1-1)2 and the symmetry breaking order parameter describing Al, Si order, Q od=(t1 0?t1 m)/Q od=(t1 0+t1 m), where t1 is the average Al occupancy on the T1 sites and t1 o and t1 m are the individual site occupancies of the T1 o and T1 m sites, respectively. The structural state of orthoclase is characterised by strain-induced modulations with large spatial variations of the modulation wavelength. No such modulations were observed in the degree of local Al, Si order. Sanidine shows mode hardening in excess of the extrapolated effect of symmetry breaking Al, Si order, which is presumably related to nonsymmetry breaking ordering between T1 and T2 sites and/or as yet unobserved short range order of the symmetry breaking ordering scheme. The possibility of an additional phase transition in K-feldspar at temperatures above 1300 K is discussed.  相似文献   

5.
Hard Mode Infrared Spectroscopy (HMIS) is used to correlate the line shifts Δω, the intensity changes ΔA and the variations of spectral line widths Γ of infrared absorption bands with the degree of Al, Si ordering, Q od, in kinetically disordered Na-feldspar. A simple relationship Δω∝ΔA∝ΔΓ∝Q od 2 was found with the phonon band around 650 cm?1 being particularly sensitive to small changes of the degree of Al, Si ordering. It is shown that the average degree of Al, Si order can be determined from HMIS with an accuracy of ca. 8 percent using 50 mg of Na-feldspar. The experimental results agree well with recent X-ray determinations using identical samples. The significance of HMIS for the study of kinetic processes in minerals is explained.  相似文献   

6.
The Si, Al LII, III and OKα emission and quantum yield spectra were obtained for 24 silicates. It was found that in minerals of a homogeneous anion composition the Si LII, III line has double-humped structure, and when in addition to SiO 4 4? ions of other composition (BeO 4 6? , AlO 4 5? etc.) are present it has triple-humped structure. The process of crystal-glass transition was studied by X-ray spectroscopy. The result is that in spite of the original form of the Si LII, III line of the mineral this line changes its structure in glass and exhibits a typical double-humped structure. The CNDO/2 approach was used to calculate the electronic structure of basic structural groups of silicates from SiO 4 4? to Si5O 16 12? by replacing one or two of the Si atoms by Be, B, Al and P. A qualitative interpretation of the X-ray spectra is presented.  相似文献   

7.
Ab initio, molecular orbital (MO) calculations were performed on model systems of SiO2, NaAlSi3O8 (albite), H2O-SiO2 and H2O-NaAlSi3O8 glasses. Model nuclear magnetic resonance (NMR) isotropic chemical shifts (δiso) for 1H, 17O, 27Al and 29Si are consistent with experimental data for the SiO2, NaAlSi3O8, H2O-SiO2 systems where structural interpretations of the NMR peak assignments are accepted. For H2O-NaSi3AlO8 glass, controversy has surrounded the interpretation of NMR and infrared (IR) spectra. Calculated δiso1H, δiso17O, δiso27Al and δiso29Si are consistent with the interpretation of Kohn et al. (1992) that Si-(OH)-Al linkages are responsible for the observed peaks in hydrous Na-aluminosilicate glasses. In addition, a theoretical vibrational frequency associated with the Kohn et al. (1992) model agrees well with the observed shoulder near 900 cm−1 in the IR and Raman spectra of hydrous albite glasses. MO calculations suggest that breaking this Si-(OH)-Al linkage requires ∼+56 to +82 kJ/mol which is comparable to the activation energies for viscous flow in hydrous aluminosilicate melts.  相似文献   

8.
Results of ab initio molecular orbital (MO) calculations provide a basis for the interpretation of structural and thermodynamic properties of crystals, glasses, and melts containing tetrahedrally coordinated Si, Al, and B. Calculated and experimental tetrahedral atom-oxygen (TO) bond lengths are in good agreement and the observed average SiO and AlO bond lengths remain relatively constant in crystalline, glassy, and molten materials. The TOT framework geometry, which determines the major structural features, is governed largely by the local constraints of the strong TO bonds and its major features are modeled well by ab initio calculations on small clusters. Observed bond lengths for non-framework cations are not always in agreement with calculated values, and reasons for this are discussed in the text. The flexibility of SiOSi, SiOAl, and AlOAl angles is in accord with easy glass formation in silicates and aluminosilicates. The stronger constraints on tetrahedral BOB and BOSi angles, as evidenced by much deeper and steeper calculated potential energy versus angle curves, suggest much greater difficulty in substituting tetrahedral B than Al for Si. This is supported by the pattern of immiscibility in borosilicate glasses, although the occurrence of boron in trigonal coordination is an added complication. The limitations on glass formation in oxysulfide and oxynitride systems may be related to the angular requirements of SiSSi and Si(NH)Si groups. Although the SiO and AlO bonds are the strongest ones in silicates and aluminosilicates, they are perturbed by other cations. Increasing perturbation and weakening of the framework occurs with increasing ability of the other atom to compete with Si or Al for bonding to oxygen, that is, with increasing cation field strength. The perturbation of TOT groups, as evidenced by TO bond lengthening predicted by MO calculations and observed in ordered crystalline aluminosilicates, increases in the series Ca, Mg and K, Na, Li. This perturbation correlates strongly with thermochemical mixing properties of glasses in the systems SiO2-M 1 n/n+ AlO2 and SiO2-M n+O n/2 (M=Li, Na, K, Rb, Cs, and Mg, Ca, Sr, Ba, Pb), with tendencies toward immiscibility in these systems, and with systematics in vibrational spectra. Trends in physical properties, including viscosity at atmospheric and high pressure, can also be correlated.  相似文献   

9.
We have measured in-situ Raman spectra of aluminosilicate glasses and liquids with albite (NaAlSi3 O8) and anorthite (CaAl2Si2O8) compositions at high temperatures, through their glass transition range up to 1700 and 2000 K, respectively. For these experiments, we have used a wire-loop heating device coupled with micro-Raman spectroscopy, in order to achieve effective spatial filtering of the extraneous thermal radiation. A major concern in this work is the development of methodology for reliably extracting the first and second order contributions to the Raman scattering spectra of aluminosilicate glasses and liquids from the high temperature experimental data, and analyzing these in terms of vibrational (anharmonic) and configurational changes. The changes in the first order Raman spectra with temperature are subtle. The principal low frequency band remains nearly constant with increasing temperature, indicating little change in the T-O-T angle, and that the angle bending vibration is quite harmonic. This is in contrast to vitreous SiO2, studied previously. Above Tg, intensity changes in the 560–590 cm?1 regions of both sets of spectra indicate configurational changes in the supercooled liquids, associated with formation of additional Al-O-Al linkages, or 3-membered (Al, Si)-containing rings. Additional intensity at 800 cm?1 reflects also some rearrangement of the Si-O-Al network.  相似文献   

10.
We report a FTIR (Fourier transform infrared) study of a set of cordierite samples from different occurrence and with different H2O/CO2 content. The specimens were fully characterized by a combination of techniques including optical microscopy, single-crystal X-ray diffraction, EMPA (electron microprobe analysis), SIMS (secondary ion mass spectrometry), and FTIR spectroscopy. All cordierites are orthorhombic Ccmm. According to the EMPA data, the Si/Al ratio is always close to 5:4; X Mg ranges from 76.31 to 96.63, and additional octahedral constituents occur in very small amounts. Extraframework K and Ca are negligible, while Na reaches the values up to 0.84 apfu. SIMS shows H2O up to 1.52 and CO2 up to 1.11 wt%. Optically transparent single crystals were oriented using the spindle stage and examined by FTIR micro-spectroscopy under polarized light. On the basis of the polarizing behaviour, the observed bands were assigned to water molecules in two different orientations and to CO2 molecules in the structural channels. The IR spectra also show the presence of small amounts of CO in the samples. Refined integrated molar absorption coefficients were calibrated for the quantitative microanalysis of both H2O and CO2 in cordierite based on single-crystal polarized-light FTIR spectroscopy. For H2O the integrated molar coefficients for type I and type II water molecules (ν3 modes) were calculated separately and are [I]ε?=?5,200?±?700?l?mol?1?cm?2 and [II]ε?=?13,000?±?3,000?l?mol?1?cm?2, respectively. For CO2 the integrated coefficient is $ \varepsilon_{{{\text{CO}}_{ 2} }} $ ?=?19,000?±?2,000?l?mol?1?cm?2.  相似文献   

11.
A detailed evaluation of the assignments given to the infrared (IR) vibrations in the lattice stretching region is presented here based on observations of the effects of various chemical substitutions in synthetic analogues of phlogopite, KMg3(AlSi3)O10(OH)2. As in previous studies, this study has confirmed that the 995, 960, and 460 cm?1 vibrations are influenced by Si, the 822 and 760 cm?1 vibrations by Al, the 915 and 725 cm?1 vibrations by Al and Si, and the 592 cm?1 vibration by OH. Contrary to previous studies, it is shown here that the 690, 495, and 375 cm?1 vibrations are strongly linked with Mg and not just Si. The 655 cm?1 band in phlogopite is attributed to an in-plane Al-O vibration rather than an Al-O-Si vibration. As a check on the band assignments made here, IR spectra were obtained for synthetic clintonite, CaMg2Al(Al3Si)O10(OH)2, as well as its chemical analogues and compared with the IR spectrum of phlogopite. The band intensities for the Si-O, Al-O, and Si-O-Mg vibrations changed in accord with the composition of clintonite. The most intense band in clintonite at 660 cm?1 appears to be associated only with Al and is assigned here to a tetrahedral Al-O-Al vibration which must be present, if not dominant, in this mineral. The near coincidence of an in-plane Al-O vibration at 655 cm?1 (phlogopite) and an in-plane Al-O-Al vibration at 660 cm?1 (clintonite) makes the identification of tetrahedral Al-Si order-disorder in trioctahedral layered silicates by IR spectroscopy very difficult. The ratio of the 822/995 cm?1 bands may, however, prove to be very useful for discerning the amount of tetrahedrally coordinated Al in these types of minerals.  相似文献   

12.
Normal coordinate calculations have been carried out on partially polymerized simple silicate crystals, including Li and Na di- and metasilicates, Li and Gd pyrosilicates, thortveitite and rankinite. In the antisymmetric Si-O stretching modes which are active at 800–1200 cm?1 in infrared spectra, Si-Obr vibrations occur at higher frequencies than Si-Onb vibrations if the bonds have equivalent strengths. However, this relationship is usually reversed when bridging oxygens are overbonded and non-bridging oxygens are underbonded in terms of Pauling bond strengths, a situation which is generally more common in crystals. An observed bimodality of the high-frequency envelope in infrared spectra of glasses in the alkali oxide-silica systems may be somewhat fortuitous, with the high frequency component (ca. 1100 cm?1) representing underbonded non-bridging oxygens and saturated bridging oxygens, and the lower-frequency component (ca. 1000 cm?1) mainly oversaturated bridging oxygens. Significant differences between crystals and glasses in the number and location of the main high-frequency infrared peaks suggest that there are short-range bonding rearrangements in the glasses, and that crystallite models are not applicable. Mid-frequency (600–800 cm?1) infrared modes in silicates more polymerized than the pyrosilicate (Si2O7) appear to be mostly antisymmetric modes in which Si rattles against bridging oxygens, rather than symmetric stretching modes.  相似文献   

13.
Pure, synthetic 2M1-muscovites (Ms) and 2M1-paragonites (Pg) prepared at 7, 13.5, and 18 kbar have been subjected to careful X-ray powder diffractometry and IR powder spectrometry. The results of X-ray studies show that the lattice constants of these micas are independent of the pressure employed in synthesizing them. Similarly, the IR powder spectra of Ms and Pg remain unaffected by the synthesis pressure. Neither the Al[4]-O-Al[4] vibrations decrease in relative intensity nor do the Si-O-Al[4] vibrations increase in intensity with increasing pressure of synthesis, as they should, if pressure-induced (Al, Si)[4] ordering had been operative. Finally, the v OH bands in Ms and Pg are also found to retain their fine structural details, regardless of the pressures employed in synthesizing these phases. In particular, the half widths of v OH in these (Al,Si)[4]-disordered micas remain constant at around 60 cm−1, compared to ∼ 10 cm−1 in (Al,Si)[4]-ordered mica margarite. In the light of this study, shortening of the b lattice parameter and progressive (Al,Si)[4] ordering with increasing pressure of synthesis of muscovites reported by Velde (1980) would appear to be anomalous. Consequently, any discussion of the effect of (Al,Si)[4] ordering on the stability of muscovite is a moot point at present.  相似文献   

14.
Normal coordinate calculations, producing synthetic infrared and Raman spectra, were carried out on melilites, pyroxenes, silica polymorphs and feldspars. Atomic motions are complex in the high-frequency Raman modes of melilites and aluminous pyroxenes. The symmetric T-Onb stretching vibrations of Si and Al tetrahedra with different numbers of bridging oxygens are separate from each other, but may combine individually with oscillation of bridging oxygens between Si and Al tetrahedra. The latter type of vibration tends to dominate as Al/Si increases. The frequencies of these vibrational components and the degree of such intermixing depend on T-O force constants, which vary greatly depending on local bonding configurations; individual bands in the high-frequency Raman cannot in general be assigned to single structural entities or fixed combinations thereof. Calculations confirm that in some Al-Si glasses such as jadeite and spodumene, i.e. those in which all Al can be tetrahedral without non-bridging oxygens, Al-O-Al linkages or linkage of more than two tetrahedra by a single oxygen, aluminum is predominantly in tetrahedral coordination. Other Al-Si glasses which are richer in aluminum or which have non-bridging oxygens may contain Al tetrahedral triclusters, non-tetrahedral Al, or both. On the basis of distinctive 450–750 cm?1 infrared bands, both silica and feldspar glasses resemble tridymite and related stuffed derivatives, not other crystalline silica polymorphs or feldspars. Either these glasses have a structure like that of tridymite on a local scale, or the disorder of the glasses causes drastic modification to the vibrations in question.  相似文献   

15.
A single-crystal of topaz was studied by Raman spectroscopy to assign the internal modes of the high-frequency range and to compare with infrared data. All active modes exhibit an important Davydov splitting (150 cm?1) but we have found a small Bethe splitting (14.5 cm?1) consistent with a very regular SiO4 tetrahedron. Because of a high value of v 1 (～920 cm?1) the Raman active modes present a mixed v 1/v 3 character. Finally the substitution of OH for F splits an A g internal mode and lead to some proper modes at 3650 cm?1, 3639 cm?1 and 1165 cm?1.  相似文献   

16.
The structure of a single crystal hydrous ringwoodite, Mg1.89Si0.98H0.30O4 synthesized at conditions of 1300?°C and 20?GPa has been analyzed. Crystallographic data for hydrous ringwoodite obtained are; Cubic with Space group: Fd3m (no. 227). a= 8.0693(5)?Å, V=526.41(9)?Å3, Z=8, Dcalc= 3.48?g?cm?3. The results of site occupancy refinement using higher angle reflections showed the existence of a small degree of Mg2+-Si4+ disorder in the structure such as (Mg1.84Si0.05□0.11)(Si0.93Mg0.05□0.02)H0.30O4. The IR and Raman spectra were measured and OH vibration spectra were observed. A broad absorption band was observed in the IR spectrum and the maxima were observed at 3160?cm?1 in the IR and at 3165?cm?1 and 3685?cm?1 in relatively sharp Raman spectra, which suggest that locations between O-O pairs around the octahedral 16c and 16d sites are possible sites for hydrogen.  相似文献   

17.
Synthetic CaAlSiO4F, the Al-F analog of titanite, has been investigated using single-crystal synchrotron diffraction experiments at Beamline X06DA (Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland) and Raman spectroscopy. The presented structural model with 40 parameters was refined against 506 unique reflections to a final R o b s of 0.026 (space group A2/a, a = 6.9120(11), b = 8.5010(10), c = 6.435(2) Å, β = 114.670(11)°, and Z = 4) and exhibits less distorted coordination polyhedra than earlier models from powder data. Vibrational spectra were calculated in harmonic approximation at the Γ point from fully relaxed energy optimisations of the crystal structure, using 3D-periodic density functional theory with Gaussian basis sets and the software CRYSTAL06. The lattice parameters of the fully relaxed structure were in good agreement with the experimental values, with the calculated values 0.8 ± 0.4 % too large; the monoclinic angle was calculated 0.4° too large. The agreement of the calculated Raman frequencies with the observed ones was very good, with standard deviation ±3 cm?1 and maximum deviations of ±7 cm?1. Furthermore, a detailed discussion of the atomic displacements associated with each Raman mode is given.  相似文献   

18.
Radiation-induced smoky color and associatedelectron paramagnetic resonance (EPR) signals develop only in potassium feldspar (KAlSi3O8) free of structurally bound molecular water. Fluid inclusion water does not influence coloration. The integrated intensity of each of the four bands (11,600, 16,200, 19,100, and 27,200 cm?1) in the optical absorption spectra are linearly correlated with the doubly-integrated intensity of a broad, asymmetric first derivative atg eff=2.027 in EPR spectra. In microcline, the EPR pattern is resolved into an asymmetric six-line pattern atg eff=2.024 and a single derivative atg eff=2.009 which, based on analogy to alkali-silicate glass, are due respectively to [SiO4/K+]2+ and a hole shared between two nonbonding oxygens on Si. We propose that structural water inhibits formation of smoky centers in feldspar by releasing atomic hydrogen during irradiation which destroys centers while diffusing towards a stable site.  相似文献   

19.
The natural occurrence of hydroxide in olivine   总被引：1，自引：0，他引：1  
Polarized infrared (IR) spectra of olivine single crystals from 17 different localities show a tremendous variability in both mode and abundance of hydroxide (OH) incorporation. Kimberlitic olivines contain the most total OH at an estimated concentration level of 976 H/106Si, whereas olivines from basalts contain the least at 3 H/106Si. Olivines of metamorphic and hydrothermal origin have widely varying concentration levels intermediate between those of basalts and kimberlites. Over 30 distinct OH absorption bands have been identified. Most of these bands are not unique to individual localities but may be found in samples from several different localities. Pleochroism is consistent among localities, but relative band intensities vary. No evidence is found for molecular H2 in olivine. Hydrous minerals have been identified in olivine by their characteristic OH absorption bands. Serpentine is commonly found and is clearly distinguishable from intrinsic OH. Talc is present in one sample. Prominent OH bands at 3572 and 3525 cm?1 are attributed to humite group minerals. San Carlos, Arizona, olivines annealed in the presence of H2O develop absorption bands which are found in natural samples, however the OH absorption spectra of these annealed olivines are not identical to those of any single natural crystal. Sharp-band OH abundances in annealed samples are an order of magnitude lower than the maximum measured in natural specimens. The mechanical properties determined from these annealed olivines may not be directly applicable to mantle olivine because both the OH sites and concentrations are different.  相似文献   

20.
Optical absorption spectra (OAS) of synthetic single crystals of the solid solution spinel sensu stricto (s.s.)–magnesioferrite, Mg(Fe3+Al1???y)2O4 (0?y?≤ 0.3), have been measured between 12 500 and 28 500?cm?1. Chemical composition and Fe3+ site distribution have been measured by electron microprobe and Mössbauer spectroscopy, respectively. Ferric iron is ordered to the tetrahedral site for samples with small magnesioferrite component, and this ordering is shown to increase with magnesioferrite component. The optical absorption spectra show a strong increase in band intensities with Fe3+→Al substitution. Prominent and relatively sharp absorption bands are observed at 25 300 and 21 300?cm?1, while less intense bands occur at 22 350, 18 900, 17 900 and 15 100?cm?1. On the basis of band energies, band intensities and the compositional effect on band intensity, as well as structural considerations, we assign the observed bands to electronic transitions in IVFe3+–VIFe3+clusters. A linear relationship (R 2= 0.99) between the αnet value of the absorption band at 21 300?cm?1 and [IVFe3+]?·?[VIFe3+] concentration product has been defined: αnet=2.2?+?15.8 [IVFe3+]?·?[VIFe3+]. Some of the samples have been heat-treated between 700 and 1000?°C to investigate the relation between Fe3+ ordering and absorption spectra. Increase of cation disorder with temperature is observed, which corresponds to a 4% reduction in the number of active clusters. Due to the high spatial resolution (??～?10?μm), the OAS technique may be used as a microprobe for determination of Fe3+ concentration or site partitioning. Potential applications of the technique include analysis of small crystals and of samples showing zonation with respect to total Fe3+ and/or ordering.  相似文献   

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