Raman Spectroscopic Study of the Molybdate Mineral Szenicsite and Comparison with Other Paragenetically Related Molybdate Minerals

Abstract

The molybdate‐bearing mineral szenicsite, Cu₃(MoO₄)(OH)₄, has been studied by Raman and infrared spectroscopy. A comparison of the Raman spectra is made with those of the closely related molybdate‐bearing minerals, wulfenite, powellite, lindgrenite, and iriginite, which show common paragenesis. The Raman spectrum of szenicsite displays an intense, sharp band at 898 cm^?1, attributed to the ν₁ symmetric stretching vibration of the MoO₄ units. The position of this particular band may be compared with the values of 871 cm^?1 for wulfenite and scheelite and 879 cm^?1 for powellite. Two Raman bands are observed at 827 and 801 cm^?1 for szenicsite, which are assigned to the ν₃(E _g ) vibrational mode of the molybdate anion. The two MO₄ ν₂ modes are observed at 349 (B _g ) and 308 cm^?1 (A _g ). The Raman band at 408 cm^?1 for szenicsite is assigned to the ν₄(E _g ) band. The Raman spectra are assigned according to a factor group analysis and are related to the structure of the minerals. The various minerals mentioned have characteristically different Raman spectra.     

Discrimination of Poly(butylenes adipate-co-terephthalate) and Poly(ethylene terephthalate) with Fourier Transform Infrared Microscope and Raman Spectroscope

ABSTRACT

The analysis of plastics and fibers is of importance to forensic scientists, especially in the investigation of trace evidence. In this study, we use Fourier transform infrared microscope and confocal Raman spectroscope to investigate two kinds of polymers: poly(butylenes adipate-co-terephthalate) and poly(ethylene terephthalate), which are very similar in structure and cannot be discriminated easily with other instruments. Infrared and Raman spectra were tentatively interpreted. The indicative peaks (937 cm^?1, 1121 cm^?1 in Infrared spectra; 996 cm^?1, 1396 cm^?1 in Raman spectra) to distinguish the two polymers were also summarized. The data in this study can help forensic scientists identify these two polymers accurately and avoid wrong certificate of authenticity. The data also offer the producer and researchers an effective and fast method to characterize and identify the poly(butylenes adipate-co-terephthalate).     

Raman spectroscopy of melamine at high pressures up to 60 GPa

In this work, the Raman scattering of melamine was studied under high pressure up to 60 GPa. The behavior of the most intensive peaks of the Raman spectrum of melamine, 677 cm^?1 and 985 cm^?1 modes, and their line widths do not show any phase transition or indication of formation of sp ³ bonds. Comparing the behavior of the line width of the Raman peaks of graphite under pressure and that of melamine leads us to conclude that the s-triasine (C–N) ring is more rigid than the C–C graphite ring. High pressure results with melamine suggest that the direct phase transition g-C₃N₄ to dense C₃N₄ phase should occur above 60 GPa.     

Raman spectra in doped cadmium oxide

Raman spectra of polycrystalline CdO-samples with electron-densities between 0.8 × 10¹⁹ and 13 × 10¹⁹ cm^?3 and mobilities between 80 and 250 cm²V^?1sec^?1 were observed at 300 and 2 K. Two first order Raman peaks are found at 404 and 345 cm^?1 while the second order spectrum is interpreted as due to the following processes: 2LO(L) near 970 cm^?1, 2LO(X) near 780 cm^?1, 2TO(X) or 2TO(L) at 480 cm^?1 and TA + TO(X) at 270 cm^?1. The 2LO(L)-peak shift to lower energiesand broadens with increasing electron density. This effect cannot be explained by existing theories.     

Effects of hydrogen flow on properties of hydrogen doped ZnO thin films prepared by RF magnetron sputtering

The hydrogen doped ZnO (ZnO:H) thin films were deposited on quartz glass substrates by radio frequency magnetron sputtering. The doping characteristics of ZnO:H thin films with varied hydrogen flow ratio were investigated. At low hydrogen flow ratio (H₂/(H₂+Ar)≤0.02), the ZnO:H thin films exhibited dominant (002) peaks from X-ray diffraction and the lattice constants became smaller. The particles were mainly a columnar structure. The particles’ size became smaller, and the island-like structure appeared on the thin films surface. In addition, the low resistivity properties of ZnO:H thin films was ascribed to the increase of the carriers concentration and carriers mobility; When the hydrogen flow ratio was more than 0.02 (M≥0.02), two absorption bands at 1400–1800 cm^?1 and 3200–3900 cm^?1 were observed from the FT-IR spectra, which indicated that the ZnO:H thin films had typical Zn–H bonding, O–H bonding (hydroxyl), and Zn–H–O bonding (like-hydroxyl). The scanning electron microscope (SEM) results show that a large number of hydroxyl agglomeration formed an island-like structure on the thin films surface. The absorption peak at about 575 cm^?1 in the Raman spectra indicated that oxygen vacancies (V_O) defects were produced in the process of high hydrogen doping. In this condition, the low resistivity properties of ZnO:H thin films were mainly due to the increasing electron concentration resulted from V_O. Meanwhile, the Raman absorption peaks at approximately 98 cm^?1 and 436 cm^?1 became weaker, and the (002) XRD diffraction peak quenched and the lattice constants increased, which shows that the ZnO:H thin films no longer presented a typical ZnO hexagonal wurtzite structure. With the increasing of hydrogen flow ratio, the optical transmittance of ZnO:H thin films in the ultraviolet band show a clear Burstein–Moss shift effect, which further explained that electron concentration was increased due to the increasing V_O with high hydrogen doping concentration. Moreover, the optical reflectance of the thin films decreased, indicating the higher roughness of the films surface. It was noteworthy that etching effect of H plasma was obvious in the process of heavy hydrogen doping.     

Variable-Temperature and High-Pressure Micro-Raman Spectra of Inorganic Artists' Pigments: Crystalline Wulfenite,Lead(II) Molybdate(VI), PbMoO4

Variable-temperature (?150°C to 600°C) and high-pressure (up to ～5 GPa) micro-Raman spectra have been obtained for the mineral wulfenite [lead(II) molybdate(VI), PbMoO₄], a main constituent of the artists' pigment, orange molybdate. The spectra were quite similar in both the temperature and the pressure studies, except for broadening and shifting of some peaks. No phase changes were detected, although there is possibly some amorphization beginning at ～600°C. The photoacoustic IR spectrum in the 1950–450 cm^?1 region is reported for characterization purposes. The long-term stability of PbMoO₄ with respect to extreme changes in both temperature and pressure illustrates the importance of orange molybdate in artwork and protective coatings.     

Investigation of L(+)-Ascorbic acid with Raman spectroscopy in visible and UV light

Abstract: Raman spectroscopy investigations of l(+)-ascorbic acid and its mono- and di-deprotonated anions (AH^? and A^2?) are reviewed and new measurements reported with several wavelengths, 229, 244, 266, 488, and 532 nm. Results are interpreted, assisted by new DFT/B3LYP quantum chemical calculations with 6-311++G(d,p) basis sets for several conformations of ascorbic acid and the anions. Raman spectra were measured during titration with NaOH base in an oxygen-poor environment to avoid fluorescence when solutions were alkaline. The ultraviolet (UV) absorption band for ascorbic acid in aqueous solution at ～247 nm was found to cause strong resonance enhancement for the ring C?C stretching mode (called B) at ～1692 cm^?1. The ascorbate mono-anion absorbs at ～264.8 nm giving Raman resonance enhancement for the same ring C–C bond stretching, downshifted to ～1591 cm^?1. Finally, for the ascorbate di-anion, absorption was found at ～298.4 nm with molar absorptivity of ～7,000 L mol^?1 cm^?1 and below ～220 nm. With UV light (244 and 266 nm), strongly basic solutions gave pronounced Raman resonance enhancement at ～1556 cm^?1. Relatively weak preresonance enhancement was seen for A^2? when excitation was done with 229 nm UV light, allowing water bands to become observable as for normal visible light Raman spectra.     

Infrared and Raman Spectroscopic Characterization of the Silicate Mineral Gilalite Cu5Si6O17 · 7H2O

Gilalite is a copper silicate mineral with a general formula of Cu₅Si₆O₁₇ · 7H₂O. The mineral is often found in association with another copper silicate mineral, apachite, Cu₉Si₁₀O₂₉ · 11H₂O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman bands are observed at 1066, 1083, and 1160 cm^?1.

The Raman band at 853 cm^?1 is assigned to the –SiO₃ symmetrical stretching vibration and the low-intensity Raman bands at 914, 953, and 964 cm^?1 may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman band at 673 cm^?1 with a shoulder at 663 cm^?1 is assigned to the ν₄ Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.     

A Vibrational Spectroscopic Study of the So-Called Healing Mineral Papagoite CaCuAlSi2O6(OH)3

ABSTRACT

Papagoite is a silicate mineral named after an American Indian tribe and was used as a healing mineral. Papagoite CaCuAlSi₂O₆(OH)₃ is a hydroxy mixed anion compound with both silicate and hydroxyl anions in the formula. The structural characterization of the mineral papagoite remains incomplete. Papagoite is a four-membered ring silicate with Cu²⁺ in square planar coordination.

The intense sharp Raman band at 1053 cm^?1 is assigned to the ν₁ (A _1g) symmetric stretching vibration of the SiO₄ units. The splitting of the ν₃ vibrational mode offers support to the concept that the SiO₄ tetrahedron in papagoite is strongly distorted. A very intense Raman band observed at 630 cm^?1 with a shoulder at 644 cm^?1 is assigned to the ν₄ vibrational modes.

Intense Raman bands at 419 and 460 cm^?1 are attributed to the ν₂ bending modes.

Intense Raman bands at 3545 and 3573 cm^?1 are assigned to the stretching vibrations of the OH units. Low-intensity Raman bands at 3368 and 3453 cm^?1 are assigned to water stretching modes. It is suggested that the formula of papagoite is more likely to be CaCuAlSi₂O₆(OH)₃ · xH₂O. Hence, vibrational spectroscopy has been used to characterize the molecular structure of papagoite.     

ß″-and ion-rich ß-alumina: Comparison of vibrational spectra and conductivity parameters

Single crystals of ß″-alumina containing Na⁺, K⁺, Ag⁺ and Tl⁺ ions are prepared and studied by Raman spectroscopy between 2 and 1000 cm^?1 in the 20–400 K temperature range. Far-infrared measurements are performed between 10 and 250 cm^?1. The Raman bands assigned to the spinel block vibrational modes are broad (Δv = 20 cm^?1); this reflects a high degree of disorder and can be related to stabilizing Mg²⁺ ions randomly distributed. In-plane cation vibrations are identified below 150 cm^?1 in infrared and Raman spectra. Potential barriers associated with this type of motion are discussed. The temperature dependence of the relevant low-frequency Raman spectra for K⁺ß″-alumina may be interpreted in terms of a small proportion of very mobile K⁺ ions. Tl⁺ spectra are discussed in terms of clusters. Finally, a comparison with literature results shows that the ß″ phase can be differentiated from t he ion-rich ß-alumina phase of the same composition.     

Vibrational Spectroscopic Characterization of the Arsenate Mineral Barahonaite: Implications for the Molecular Structure

The mineral barahonaite is in all probability a member of the smolianinovite group. The mineral is an arsenate mineral formed as a secondary mineral in the oxidized zone of sulphide deposits. We have studied the barahonaite mineral using a combination of Raman and infrared spectroscopy. The mineral is characterized by a series of Raman bands at 863 cm^?1 with low wavenumber shoulders at 802 and 828 cm^?1. These bands are assigned to the arsenate and hydrogen arsenate stretching vibrations. The infrared spectrum shows a broad spectral profile. Two Raman bands at 506 and 529 cm^?1 are assigned to the triply degenerate arsenate bending vibration (F ₂, ν₄), and the Raman bands at 325, 360, and 399 cm^?1 are attributed to the arsenate ν₂ bending vibration. Raman and infrared bands in the 2500–3800 cm^?1 spectral range are assigned to water and hydroxyl stretching vibrations. The application of Raman spectroscopy to study the structure of barahonaite is better than infrared spectroscopy, probably because of the much higher spatial resolution.     

Raman spectroscopic study of the antimonate mineral lewisite (Ca,Fe, Na)2(Sb,Ti)2O6(O,OH)7

The mineral lewisite, (Ca, Fe, Na)₂(Sb, Ti)₂O₆(O, OH)₇, an antimony-bearing mineral, has been studied by Raman spectroscopy. A comparison is made with the Raman spectra of other minerals, including bindheimite, stibiconite, and roméite. The mineral lewisite is characterised by an intense sharp band at 517 cm^?1 with a shoulder at 507 cm^?1 assigned to SbO stretching modes. Raman bands of medium intensity for lewisite are observed at 300, 356, and 400 cm^?1. These bands are attributed to OSbO bending vibrations. Raman bands in the OH stretching region are observed at 3200, 3328, 3471 cm^?1, with a distinct shoulder at 3542 cm^?1. The latter is assigned to the stretching vibration of OH units. The first three bands are attributed to water stretching vibrations. The observation of bands in the 3200–3500 cm^?1 region suggests that water is involved in the lewisite structure. If this is the case then the formula may be better written as (Ca, Fe²⁺, Na)₂(Sb, Ti)₂(O, OH)₇ xH₂O.     

Enhanced Upconversion Luminescence of Erbium–Nitrogen-Doped Zinc Oxide Nano-Wires by Implantation of Ytterbium Ions

Erbium–nitrogen codoped zinc oxide nanowires of ytterbium-doped are prepared by thermal evaporation and ion implantation methods. Ytterbium ions are doped into nanowires at a fluence of (0, 1, 3, 5, and 9) × 10¹⁵ cm^?2. Microstructural and optical properties of specimen are investigated by X-ray diffractometer, absorption spectra, Raman, and upconversion photoluminescence examinations. Upconversion photoluminescence emissions at 550 nm and 660 nm are obtained under 980-nm light excitation. Both intensities of green and red peaks are enhanced by the introduction of ytterbium ions. When ytterbium ion fluence is 5 × 10¹⁵ cm^?2, light emission intensity reaches maximum value. The energy transfer and cross-relaxation processes are responsible for the change of emission intensity.     

Study of the electrochemical performance of VO2+/VO2 + redox couple in sulfamic acid for vanadium redox flow battery

The present work was performed in order to evaluate sulfamic acid as the supporting electrolyte for VO²⁺/VO₂ ⁺ redox couple in vanadium redox flow battery. The oxidation process of VO²⁺ has similar electrochemical kinetics compared with the reduction process of VO₂ ⁺. The exchange current density and standard rate constant of VO²⁺/VO₂ ⁺ redox reaction on a graphite electrode in sulfamic acid are determined as 7.6?×?10^?4 A cm^?2 and 7.9?×?10^?5 cm s^?1, respectively. The energy efficiency of the cell employing sulfamic acid as supporting electrolyte in the positive side can reach 75.87 %, which is adequate for redox flow battery applied in energy storage. The addition of NH₄ ⁺ to the positive electrolyte can enhance the electrochemical performance of the cell, with larger discharge capacity and energy efficiency. The preliminary exploration shows that the vanadium sulfamate electrolyte is promising for vanadium redox flow battery and is worthy of further study.     

Surface-enhanced Raman scattering spectroscopic analysis of Saposhnikovia divaricata decoction

ABSTRACT

Surface-enhanced Raman scattering spectroscopy was employed to analyze the biochemical composition of the Saposhnikovia divaricata decoction, which is a common traditional Chinese medicine. No reliable Raman peak was observed in traditional Raman spectra of Saposhnikovia divaricata decoction. However, 12 main Raman peaks (534, 616, 648, 685, 730, 781, 850, 958, 1242, 1319, 1460, and 1571 cm^?1) were observed in the surface-enhanced Raman scattering spectroscopy spectra from the mixture of silver colloids with Saposhnikovia divaricata decoction as a result of the silver colloid enhanced effects on the Raman scattering of Saposhnikovia divaricata decoction. The results demonstrated that the surface-enhanced Raman scattering spectroscopy may provide a new kind of non-destructive, accurate, direct, and fast detecting method for the Saposhnikovia divaricata decoction or other traditional Chinese medicine in the form of decoction.     

Raman Spectroscopic Characterization of the Alkaloid Dihydrochelerytrine Extracted from Roots of Zanthoxylum stelligerum (Turcz)

ABSTRACT

Raman spectroscopy has been used successfully in the identification of the alkaloid dihydrochelerytrine due to the assignment of specific key marker bands in the region between 1000 and 1600 cm^?1. The Raman spectrum obtained from the crude hexane extract of the roots of Zanthoxylum stelligerum, and excited with 1064 nm, provides very good molecular information, as can be seen by the comparison between the Raman spectra of the standard dihydrochelerytrine and the crude extract, where the keymarker bands are present in both spectra.     

Effect of uniaxial pressure on the Raman spectra of fluoro perovskites containing manganese with sodium or potassium

ABSTRACT

Perovskite structured mixed metal fluorides containing manganese/sodium or potassium have been synthesized in pure form by a greener precipitation route and characterized by high-resolution powder X-ray diffraction and Raman spectroscopy techniques. While all the reflections in the powder X-ray diffraction pattern of potassium manganese fluoride could be indexed in cubic symmetry with a = 4.1889 Å, sodium manganese fluoride showed reflections at positions typical of orthorhombic symmetry (Pnma space group) with a = 5.751, b = 8.008, and c = 5.548 Å. Potassium manganese fluoride in powder form showed bands at 209, 291, 386, 558, 621, and 733 cm^?1 in the Raman spectrum at room temperature. All these bands disappeared and second-order band at 1151 and 1298 cm^?1 emerged when the powders were compacted under pressure ranging between 1 and 4 tons (uniaxial). A similar change was noticed for sodium manganese fluoride in which bands at 1099, 1149, 1203, and 1286 cm^?1 were observed for the compacted samples. The response of the vibrational modes of these compounds to uniaxial pressure revealed the existence of large structural disorder in them. Additionally, the need for the extreme care to collect and interpret Raman data of polycrystalline samples of these systems has been illustrated through this study.     

Excitation and Emission Spectra of Cs2NaLnCl6 Crystals Using Synchrotron Radiation

ABSTRACT

The visible emission and vacuum ultraviolet excitation spectra of the series Cs₂NaLnCl₆ (Ln = Y, Nd, Sm, Eu, Tb, Er, Yb) and Cs₂NaYCl₆:Ln³⁺ (Ln = Sm, Er) have been recorded using synchrotron radiation at room temperature, and in some cases at 10 K. The excitation spectra comprise features associated with charge transfer, excitation from the valence to conduction band, and impurity bands. No d–f emissions were observed for these Ln³⁺ ions, so that the emission bands comprise intraconfigurational 4f ^N –4f ^N transitions and impurity bands, whose natures are discussed. Theoretical simulations of the f–d absorption spectra have been included. The comparison with data from the synchrotron at Desy enables a comprehensive account of the ground (or vibrationally excited ground for Ln²⁺) states of the Ln³⁺ 4f ^N , Ln³⁺ 4f ^N?15d, and Ln²⁺ 4f ^N+1 configurations relative to the valence and conduction bands of Cs₂NaLnCl₆, for which the band gaps are between 6.6 and 8.1 eV.     

Raman Spectroscopy Investigation of Nano Hydroxyapatite Doped with Yttrium and Fluoride Ions

In this study, nano hydroxyapatite doped with yttrium (2.5, 5, and 7.5 mol%) and fluoride (2.5 mol%) ions were synthesized by precipitation method and sintered at 900°C, 1100°C, and 1300°C. Raman spectroscopy was applied to track the structural modifications in pure and doped hydroxyapatites. The results showed that the main characteristic band of pure hydroxyapatite at 963 cm^?1 was not affected significantly by ion doping but exhibited higher intensity with increasing sintering temperature. Due to fluoride substitution, the 1048 and 1034 cm^?1 bands of pure hydroxyapatites appeared with a wavenumber shift in the spectra of ion-doped hydroxyapatites. The 333 cm^?1 band of pure hydroxyapatite disappeared and an additional calcium–fluor bond at 322 cm^?1 was observable in ion-doped hydroxyapatites. Two fluorescence bands at 770 and 697 cm^?1, which were also observed in the spectra of pure hydroxyapatites, shifted to higher wavenumbers in the spectra of ion-doped hydroxyapatites. This was considered to result from the perturbation in the hexagonal structure of hydroxyapatite due to yttrium and fluoride codoping.     

Raman Spectroscopic Study of the Copper Silicate Mineral Apachite Cu9Si10O29 · 11H2O

ABSTRACT

Apachite, Cu₉Si₁₀O₂₉ · 11H₂O, is a mineral named after the American Indian Apache tribe. Raman and infrared spectroscopy have been used to characterize the molecular structure of apachite. The structure of the mineral shows disorder, which is reflected in the difficulty in obtaining quality Raman spectra. Raman spectroscopy clearly shows the presence of OH units in the apachite structure, which attests the formula to be not correct. Both Raman and infrared spectroscopy show the presence of water in the apachite structure. Different water molecules are present with different hydrogen bonding strengths. A suggested formula might be Cu₉Si₁₀O₂₃(OH)₁₂ · 5H₂O.

The Raman band at 967 cm^?1 is assigned to the –SiO₃ symmetrical stretching vibration and the bands at 997 and 1096 cm^?1 are assigned to the ν₃ –SiO₃ antisymmetric stretching vibrations. An intense Raman band at 673 cm^?1 with a shoulder at 663 cm^?1 is assigned to the ν₄ Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of apachite.