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1.
For the purpose of determining the orientation of the OH? dipole in an optically anisotropic crystal, distribution of polarized IR absorbance is formulated under Fourier transform microspectroscopy. The formulatd absorbance distribution suggests that the degree of pleochroism of absorbance depends on the angle between the orientation of the OH? dipole and the principal orientation of the optically anisotropic crystal. As its application, the general orientation of the OH? dipole in topaz is determined to be inclined 27.3° from the c-axis in (010).  相似文献   

2.
In order to investigate the behaviour of proton in brucite under pressure, polarized IR absorption spectra and polarized absorbance distributions of (001) and (110) oriented single crystal of brucite under high pressure were measured by Fourier transform polarized infrared microspectroscopy with diamond anvil cell. A pressure-induced absorption peak at 3645 cm−1 observed under pressures over 2.9 GPa was confirmed to be due to a secondarily formed OH dipole. Polarized absorbance distribution measured under pressure of (110) suggests that the secondary OH dipole is oriented 136.0° to c-axis under 5.3 GPa. Isotropic absorbance distribution of (001) suggests that the secondary OH dipole is disorderly trifurcated. Abrupt onset of the secondary peak and its reverse pleochroism suggest that the process of secondary OH dipole formation is due to proton transfer between layers in brucite. The calculated orientation of the secondary OH dipole consistent with the O-H···O′ angle revealed by neutron diffraction supports the existence of proton transfer along H···O′. The secondary OH dipole implies a new site of proton in brucite under pressure. Received: 6 March 1997 / Revised, accepted: 9 June 1997  相似文献   

3.
The theoretical infrared (IR) and Raman spectra of bayerite (β-Al(OH)3) are computed in the density functional theory framework, using the linear response theory. The results are consistent with the occurrence of six non-equivalent OH groups in a bayerite structure with space group P21/n. Similar to gibbsite, the transmission powder IR spectrum of bayerite in the region of the OH stretching bands is found to depend on the shape of particles. In particular, the broadening of the strong band observed at about 3,460 cm−1 in the spectrum of Al hydroxides is related to the electrostatic charges occurring at the surface of the polarized dielectric particles. The experimental correlation observed between the shape of this band and morphological parameters has therefore a physical, instead of chemical, origin.  相似文献   

4.
Infrared spectroscopy is a powerful technique for probing H-species in nominally anhydrous minerals, and a particular goal of considerable efforts has been providing a simple yet accurate method for the quantification. The available methods, with either polarized or unpolarized analyses, are usually time-consuming or, in some cases, subjected to larger uncertainty than theoretically expected. It is shown here that an empirical approach for measuring the concentration, by determining three polarized infrared spectra along any three mutually perpendicular directions, is theoretically and in particular experimentally correct. The theoretical background is established by considering the integrated absorbance, and the experimental measurements are based on a careful evaluation of the species and content of H in a series of gem-quality orthogonal, monoclinic and triclinic crystals, including olivine, orthopyroxene, clinopyroxene, orthoclase and albite (natural and H-annealed). The results demonstrate that the sum of the integrated absorbance from two polarized spectra along two perpendicular directions in any given plane is a constant, and that the sum of the integrated absorbance from three polarized spectra along any three orthogonal directions is of essentially the same accuracy as that along the principal axes. It is also shown that this method works well, with a relative accuracy within 10%, even at some extreme cases where the sample absorption bands are both intense and strongly anisotropic.  相似文献   

5.
In-situ IR measurements of OH species in quartz at high temperatures   总被引：1，自引：0，他引：1  
The nature of OH species in natural clear quartz was investigated by means of in-situ IR measurements over the temperature range –185 to 1000 °C. Reversible thermal behavior of OH species was examined for a sample pre-heated to 1000 °C for 1 hour. At room temperature, the IR spectrum of the quartz sample examined includes an intense absorption peak at 3379 cm–1 which has been assigned to an OH stretching vibration associated with Al substituting for Si (OH(Al)). The major spectral changes of the OH(Al) bond involve a systematic shift of its peak position and a decrease in its integral absorbance with temperature. A quasi-linear increase of the peak position from –185 to 400 °C is interpreted to be due to the change in the vibrational frequency of OH(Al) with hydrogen bond (H bond) distance. At higher temperatures, the IR frequency shows only a slight change, indicating a small influence of the H bond. On the other hand, the gradual decrease of the integral absorbance of OH(Al) with temperature indicates a decrease of this defect’s molar absorptivity without any reduction in defect concentration. This is interpreted to result from a decrease in dipole moment of OH(Al) with temperature. A sudden shift of the vibrational frequency from 3396 to 3386 cm–1 between 550 and 560 °C and a constant value of the integral absorbance from 535 to 570 °C were considered to be related to the change in H bond distance during the structural transformation of α-quartz to its β-form. The local environment of OH(Al) begins to change at temperatures below 570 °C, where the crystallographic α–β transition occurs. Received: 18 February 1998/ Accepted: 10 July 1998  相似文献   

6.
Far-infrared absorbance spectra were collected from CaGeO3 with a metastable orthorhombic perovskite structure from 0 to 24.4 GPa. The absorbance data are compatible with a reflectance spectrum which was collected at ambient conditions from a polished, densely compacted polycrystal. The reflectance spectrum shows 18 IR modes from 155 to 786 cm?1. A detailed model for the density of states constructed from these new data results in accurate calculation of heat capacity and new data on entropy. Peak positions increase linearly with pressure. Mode Grüneisen parameters (ranging from 0.72–1.56) decrease almost linearly with increasing mode frequency which is consistent with deformations of the oxygen sublattice dominating the lattice vibrations. Neither discontinuous changes in the number of modes nor in these frequencies nor in band widths are observed at pressures up to 24.4 GPa. Thus, conversion to the tetragonal phase at ～12 GPa is not indicated.  相似文献   

7.
Synthetic Co-doped quartz was grown hydrothermally in steel autoclaves at the Technological Center of Minas Gerais (CETEC), Brazil. The quartz samples, originally yellow in the as-grown state acquired blue coloration after prolonged heat treatment times at 500°C near the alpha–beta transition temperature. UV–VIS–NIR absorption spectroscopy shows the characteristic spectra of Co3+ before heat treatment. After heat treatment, the optical absorption spectrum is dominated by two split-triplet bands the first in the near infrared region centered at about 6,700 cm−1 (1,490 nm) and the second in the visible spectral range at about 16,900 cm−1 (590 nm). Both split-triplet bands are typical for Co2+ ions in tetrahedral coordination environments. From the absence of electron paramagnetic resonance (EPR) spectra, we conclude that the Co2+ found in the optical absorption spectra of the blue quartz is not due to an isolated structural site in the quartz lattice. Instead, the blue color is associated with electronic transitions of Co2+ in small inclusions in which the Co site has tetrahedral symmetry. The non-observation of polarization-depend optical absorption spectra is also in agreement with this model. The results for Co2+ in quartz are different from Co-bearing spinel and staurolite and other silicates like orthopyroxene, olivine, and beryls. The formation process of the color center is discussed.  相似文献   

8.
Subtle variations of frequencies in the infrared (IR) absorption spectra of beryl have been predicted based on the coordination between extra-framework cations and water molecules in two orientations (referred to as type I and type II) trapped within the channel. In this study, the polarized IR spectra of hydrated synthetic beryl and natural beryl were measured to clarify the relationships between the frequencies of the absorption bands and the coordination states of type II water. Na+ was assumed to be the predominant cation coordinated to type II water in our samples, as determined by chemical analyses. These measurements revealed a clear quantitative linear relationship in absorbance between bands at 3,602 and 1,619 and at 3,589 and 1,631 cm−1. On the basis of experimental and theoretical studies, we assigned these pairs of bands to the ν1 and ν2 modes of doubly coordinated type II H2O and to singly coordinated type II H2O, respectively. These assignments were supported by IR measurements of annealed natural beryl. We also conducted dehydration studies of natural beryl, in which two observed dehydration peaks, at 600 and 750°C, suggested the dehydration of type I and type II water, respectively.  相似文献   

9.
景德镇地区高岭石红外光谱分析   总被引：3，自引：0，他引：3  
采用红外光谱实验结合氢氟酸化学处理方法深入研究景德镇地区高岭石结构特征。通过解析红外光谱图确定该区高岭石为无序高岭石范畴,其结构中含有似地开石结构BCBCBC的八面体空位取代。通过对比氢氟酸处理前后的红外图谱,分析出该地区高岭土不含有地开石和珍珠石这两种多型。实验表明红外光谱分析对高岭土中存在的次要矿物伊利石不灵敏,而利用氢氟酸处理可以有效地鉴别,因而提出了一种利用红外光谱鉴定高岭石-伊利石混合物相的新方法。  相似文献   

10.
Principles of quantitative absorbance measurements in anisotropic crystals   总被引：1，自引：0，他引：1  
The accurate measurement of absorbance (A=-log T; T=I/I 0) in anisotropic materials like crystals is highly important for the determination of the concentration and orientation of the oscillator (absorber) under investigation. The absorbance in isotropic material is linearly dependent on the concentration of the absorber and on the thickness of the sample (A=?·c·t). Measurement of absorbance in anisotropic media is more complicated, but it can be obtained from polarized spectra (i) on three random, but orthogonal sections of a crystal, or (ii) preferably on two orthogonal sections oriented parallel to each of two axes of the indicatrix ellipsoid. To compare among different crystal classes (including cubic symmetry) it is useful to convert measured absorbance values to one common basis (the total absorbance A tot), wherein all absorbers are corrected as if they were aligned parallel to the E-vector of the incident light. The total absorption coefficient (a tot=A tot/t) is calculated by $$\left( {\text{i}} \right)a_{{\text{tot}}} = \sum\limits_{i = 1}^3 {(a_{\max ,i} + a_{\min ,i} )} /2, {\text{or}} {\text{by}} {\text{(ii) }}a_{{\text{tot}}} = a_x + a_y + a_z .$$ Only in special circumstances will unpolarized measurements of absorbance provide data useful for quantitative studies of anisotropic material. The orientation of the absorber with respect to the axes of the indicatrix ellipsoid is calculated according to A x/A tot=cos2 (x < absorber), and analogously for A yand A z. In this way, correct angles are obtained for all cases of symmetry. The extinction ratio of the polarizer (Pe=I crossed/I parallel) has considerable influence on the measured amplitude of absorption bands, especially in cases of strong anisotropic absorbance. However, if Pe is known, the true absorbance values can be calculated even with polarizers of low extinction ratio, according to A max=?log[(T max,obs?0.5·Pe·T min,obs)/(1?0.5·Pe)], and similar for A min. The theoretical approach is confirmed by measurements on calcite and topaz.  相似文献   

11.
Water content of quartz in and around a greenschist facies mylonitic shear zone located in the western Adirondacks was analyzed by micro-FTIR spectroscopy. The shear zone is within a pegmatitic dike, which cuts across a granitic gneiss. The thickness of the shear zone varies along strike from 15 cm wide and encompassing all of the pegmatite dike at its northern most exposure to 5 cm wide approximately 10 m south, along strike. Microstructures, including quartz ribbons and recrystallized grains, indicate quartz and feldspar within the mylonite underwent dislocation creep. Infrared spectral analysis was carried out using a Nicolet micro-FTIR on mylonitic quartz ribbons, pegmatitic quartz and gneissic quartz. A small aperture size (56 μm by 50 μm) for the IR beam allowed optically clear regions of the quartz grains to be analyzed without any contribution from grain boundaries. The smallest dimension of the quartz ribbons is 0.3 mm, whereas the pegmatitic quartz has a grain size of 3 to 5 cm. Results show mylonitic quartz ribbons contain the most water (320 H:106 Si average, range of 50 to 1120 H:106 Si); pegmatite quartz contains much less water (30 H:106 Si average, range of 20–40 H:106 Si) and the gneissic quartz contained an intermediate amount (200 H:106 Si average, range of 20 to 870 H:106 Si). These data indicate that water was preferentially incorporated into the deformed quartz ribbons.  相似文献   

12.
Polarized IR spectra of planeparallel (0001) plates of synthetic smoky quartz, with E rotating around [0001], show that the absorption figures of OH– related absorption bands at 3380 (room temperature), 3365 and 3305 cm–1 (liquid nitrogen temperature, -196° C) are strongly anisotropic and violate the trigonal symmetry of low quartz. This effect is correlated with a non-uniform substitution of Si by Al on the three symmetrically equivalent Si sites, as revealed by EPR measurements. Random distribution of Al over the three Si sites, obtained by dry annealing of the samples in air, yields isotropic absorption figures in the (0001) plates. It is thus experimentally evident that the absorption bands at 3380, 3365 and 3305cm–1 are caused by the OH– stretching vibrations coupled with Al substituting for Si. For each experimentally determined integral absorption coefficient of the three absorption bands a theoretical absorption coefficient was calculated, based on the symmetry of low quartz and the given Al distribution. This was done for various orientations of the OH– dipoles with respect to the a axes of low quartz. By comparing the experimentally determined and calculated absorption coefficients, the orientation of the corresponding OH– dipoles with respect to the a axes could be determined.  相似文献   

13.
天然紫晶与合成紫晶的鉴别是国内外珠宝鉴定实验室的一个难题,前人主要从双晶、色带、包裹体、红外吸收光谱特征等方面开展了研究。在利用红外光谱鉴别天然紫晶与合成紫晶时,不同的学者尚对3595cm-1或3543cm-1吸收峰作为诊断性还是指示性的判据存在不同认识。本文系统采集了典型的天然紫晶与合成紫晶样品,研究了利用红外光谱测试技术鉴别天然紫晶与合成紫晶的局限性,并尝试将偏振拉曼光谱应用于紫晶成因鉴别。结果表明:利用3595cm-1、3543cm-1红外吸收峰进行紫晶鉴别仅具有指示性意义,不能作为决定性的判定依据,偏振拉曼光谱可作为重要的补充。天然紫晶的偏振拉曼光谱(偏振方向:HH)均出现400cm-1的拉曼峰,而该峰在合成紫晶偏振拉曼光谱中缺失;合成紫晶的偏振拉曼光谱(偏振方向:HH)均具有795cm-1、448cm-1的拉曼峰,而这两个峰在天然紫晶偏振拉曼光谱中缺失。偏振拉曼光谱产生差异的原因可能与天然紫晶和合成紫晶内部晶格变形程度的不同有关。本文揭示的400cm-1、448cm-1和795cm-1偏振拉曼峰可作为鉴别紫晶成因的新依据。  相似文献   

14.
Infrared (IR) and nearinfrared (NIR) absorption spectra of hydrous and F-rich topazes were measured to assign an OH bending mode of topaz. Three absorption peaks at 1165, 3650, and 4803 cm−1 are assigned to OH related absorption peaks. Since a peak at 4803 cm−1 can be assigned to a combination mode of 1165 and 3650 cm−1, the 1165 cm−1 peak is harmonic with the 3650 cm−1 peak. Polarized IR absorption spectra of (100), (010), and (001) planes of the hydrous topaz were measured to examine IR active orientation of the 1165 cm−1 OH related mode. Three pleochroic distributions of the absorption peak at 1165 cm−1 on (100), (010), and (001) planes indicate an active orientation of the 1165 cm−1 OH related mode. The IR active orientation of the 1165 cm−1 OH related mode in topaz is normal to the OH dipole. The orthogonality and harmonic combination mode indicate that the 1165 cm−1 peak is OH bending mode. The active orientation of OH bending mode is polarized in the plane normal to the OH dipole. The polarization suggests that anisotropic thermal vibration of protons on the hydroxyl is maximum along the IR active orientation. Received: August 16, 1996 / Revised, accepted: April 20, 1997  相似文献   

15.
Water plays an important role in nearly every aspect of geological processes as well as in the evolution of planetary bodies. Chang E-3 NIR spectra appeared weak peak of OH in the vicinity of signal 1.4 μm, it may represent the presence of water. In order to quantitatively calculate the water content, apatite as the research object in the paper. Through analyzing and validating the infrared spectrum correlation between 1.4 μm and 2.8 μm of the structure water in the apatite, we obtained its molar absorption coefficient in the infrared spectrum of 1.4 μm. IR spectra were collected on oriented. When the light vector E is parallel to the c-axis of the apatite crystal, H2O concentration in apatite can be related to measured IR absorbance as follows: C=ωA/ερd, which based on Beer-Lambert’s law. This result can provide reference for the interpretation of Chang E-3 near-infrared spectral data of water signal. This method can provide the basis for the quantitative calculation of structure water in the near infrared spectrum in other moon minerals.  相似文献   

16.
The mineral ussingite, Na2AlSi3O8(OH), an interrupted tectosilicate, has strong hydrogen bonding between OH and the other nonbridging oxygen atom in the structure. Infrared spectra contain a strongly polarized, very broad OH-stretching band with an ill-defined maximum between 1500 and 1800 cm–1, and a possible OH librational bending mode at 1295 cm–1. The IR spectra confirm the orientation of the OH vector within the triclinic unit cell as determined from X-ray refinement (Rossi et al. 1974). There are three distinct bands in the 1H NMR spectrum of ussingite: a predominant band at 13.5 ppm (TMS) representing 90% of the structural hydrogen, a second band at 15.9 ppm corresponding to 8% of the protons, and a third band at 11.0 ppm accounting for the remaining 2% of structural hydrogen. From the correlation between hydrogen bond length and 1H NMR chemical shift (Sternberg and Brunner 1994), the predominant hydrogen bond length (H...O) was calculated to be 1.49 Å, in comparison to the hydrogen bond length determined from X-ray refinement (1.54 Å). The population of protons at 15.9 ppm is consistent with 5–8% Al–Si disorder. Although the ussingite crystal structure and composition are similar to those of low albite, the bonding environment of OH in low albite and other feldspars, as characterized through IR and 1H NMR, is fundamentally different from the strong hydrogen bonding found in ussingite.  相似文献   

17.
A quantum-mechanical calculation of the zone-centre phonon spectrum of beryl has been performed, by using an hybrid HF/DFT Hamiltonian (B3LYP). An excellent agreement with the experiment has been obtained, being the difference between the calculated and the experimental vibrational frequencies (Raman, IR-TO and IR-LO) less than 5 cm?1 on average. In the few cases where a relatively large disagreement between calculated and experimental data is observed, an explanation can be found which attributes the reason of the discrepancies to the experimental data rather than to the calculated ones. The calculation (i) allows the identification, in the experimental spectra, of the peaks corresponding to fundamental modes, overtones, combination bands and leakage; (ii) solves problems of band assignements due to the presence of LO–TO splitting in the IR spectra; (iii) provides the frequencies of silent modes; (iv) permits a full analysis of the atomic motion corresponding to each normal mode.  相似文献   

18.
Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structural studies of aluminosilicate glasses. Both techniques are sensitive to small-scale (<15 Å) structural features that amount to units of several SiO4 tetrahedra. Application of IR spectroscopy has, however, been limited by the more complex nature of the IR spectrum compared with the Raman spectrum, particularly at higher frequencies (1200–800 cm?1) where strong antisymmetric Si-O and Si-O-Si absorptions predominate in the former. At lower frequencies, IR spectra contain bands that have substantial contributions from ‘cage-like’ motions of cations in their oxygen co-ordination polyhedra. In aluminosilicates these bands can provide information on the structural environment of Al that is not obtainable directly from Raman studies. A middle frequency envelope centred near 700 cm?1 is indicative of network-substituted AlO4 polyhedra in glasses with Al/(Al+Si)>0·25 and a band at 520–620cm?1 is shown to be associated with AlO6 polyhedra in both crystals and glasses. The IR spectra of melilite and melilite-analogue glasses and crystals show various degrees of band localization that correlate with the extent of Al, Si tetrahedral site ordering. An important conclusion is that differences in Al, Si ordering may lead to very different vibrational spectra in crystals and glasses of otherwise gross chemical similarity.  相似文献   

19.
《Quaternary Science Reviews》2003,22(10-13):1139-1143
As part of a systematic palaeohydrological reconstruction of lake level fluctuations during the Last Glacial Maximum, a transect of cores from ancient Lake Xinias in central Greece has already been studied with respect to pollen, sediment and mineral magnetic analyses. The chronology was based on 14C AMS dating of terrestrial plant macrofossil remains from peat and clayey peat (Palaeogeog. Palaeoclimatol. Palaeoecol. 158 (2000) 65). This site thus provides an opportunity for the comparison of fine grain optically stimulated luminescence (OSL) ages of water–lain sediments with an independent chronology. We present here infrared (IR), post-IR blue and blue OSL characteristics of the fine grain sediments from Lake Xinias and a preliminary comparison with independent ages. The equivalent doses based on the IR results are about 40% of those based on post-IR blue stimulation, which in turn are 10–15% below those based on quartz OSL. We discuss the ages derived from the 3 signals in terms of the independent chronology, and draw conclusions about initial bleaching of the quartz and feldspar components, and the reliability of the post-IR blue signal as a chronometer.  相似文献   

20.
The shock-metamorphosed quartz exhibits thermal luminescence (TL) with maxima at 365 nm, 470 nm and 610–680 nm. By electron paramagnetic resonance (EPR) analysis E1 type electron centers and hole centers have been found which originate from vacancies including those from the substitution of Al3+ and/or Fe3+, for Si4+. The EPR and TL spectra may be interpreted mainly in terms of vacancy type defects associated with dislocations in the crystal structure of quartz.  相似文献   

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