Additional Raman Bands Research Articles

Pyrrhotites in asteroid 162173 Ryugu: Records of the initial changes on their surfaces with aqueous alteration

The surface chemistry of pyrrhotites from intact particles directly collected from asteroid (162173) Ryugu was investigated by micro-Raman spectroscopy. The Raman peak characteristic to pyrrhotite was observed at around 115 cm−1 in Ryugu pyrrhotites, similar to freshly cleaved surfaces of terrestrial pyrrhotites. Additional Raman bands centered at around 220, 275, and 313 cm−1 with broadened features were also detected from the Ryugu pyrrhotites. The set of Raman bands at 220 and 275 cm−1 was assigned to typical Fe-S stretching vibrations of ν2 (225 cm−1) and ν1 (275 cm−1). These bands are not clearly observed in bulk crystals of pyrrhotite but appear in its nanoparticulate phase. These bands are ordinarily seen in amorphous monosulfides that formed under low oxygen fugacity (fO2) conditions in nature, indicating that the structural alteration of pyrrhotite surfaces occurred heterogeneously on the nanoscale under low fO2 conditions. Further, the Raman band at 313 cm−1 was attributed to a characteristic tetrahedral bonding of Fe(III) in the lattice of FeII1-3xFeIII1-2xS, followed by the local breakdown of the crystal lattice structures from planar bonding with Fe(II). In addition, some areas of the Ryugu pyrrhotite grains showed corroded structures with iridescence. Furthermore, assemblages of magnetite particles were also preferentially observed on small areas of the likely-dissolved pyrrhotite crystals in phyllosilicate matrices. These characteristic features in the Raman spectra and in corroded structures of Ryugu pyrrhotites record changes in the local environmental conditions via aqueous alteration. The corrosion of pyrrhotite crystals followed by the preferential formation of magnetite particles by asteroidal water is the likely product of dissolution of Fe(II) from the pyrrhotite surface and its oxidative precipitation in microchemical environments on the Ryugu parent body.

Description of an original molecular ordering process into a disordered crystalline form: the atypical low-temperature transformation of the disordered form III of linezolid.

Form III of linezolid was prepared by heating the commercial form above 150 °C and subsequently analyzed upon cooling down to -160 °C, by low- and high-frequency Raman spectroscopy, differential scanning calorimetry and powder X-ray diffraction (PXRD). It was observed that form III was preserved down to 0 °C. At lower temperatures a soft mode was clearly detected by low-frequency Raman spectroscopy associated with the detection of additional Raman bands distinctive of additional intermolecular H-bond interactions. Raman spectroscopy investigations performed in a wide frequency range revealed a continuous transformation characterized by both displacive and order-disorder signatures. By contrast, PXRD highlighted the absence of symmetry breaking, Bragg peaks being still indexed in the same unit cell from room temperature down to -160 °C. Additionally, a significant broadening of Bragg peaks was observed with decreasing temperature interpreted as being a consequence of a distribution of frozen molecular conformations.

Deuterated PET: The new verification target of the Raman spectrometer for the MMX mission to explore Phobos

AbstractJAXA's upcoming MMX (Martian Moons eXploration) mission will deliver a small rover to Phobos, to explore its surface complementary to the MMX orbiter and the sample return lander. On board this rover is a Raman spectrometer, the RAX Instrument (RAman Spectrometer for MMX), a payload to science. RAX has been designed for being capable to analyze the mineral composition of the Phobos' surface, in order to help reveal the nature and distribution of materials on the surface and ultimately the origin and evolution of the moon. Attached to MMX spacecraft, with direct view from the RAX instrument, a polyethylene terephthalate (PET) target will be placed for on‐ground and during cruise, spectral instrument performances verification, before the MMX rover is released and dropped to the Phobos surface for developing its scientific tasks. A novel deuterated PET material was proposed as verification target (VT) to check the spectral instrument performances. INTA‐CAB developed, manufactured and qualified for the MMX‐RAX space mission, 13 mm diameter and 2‐mm thick pellets of this material, which incorporates two relevant improvement characteristics: reduction in fluorescence and additional Raman bands with regard to ordinary PET used with this purpose. The material was selected as RAX VT and delivered to DLR for performance tests and later integration into the MMX rover together with the RAX flight model. The RAX VT will be critical to check the instrument performances during the several months cruise phase after launch and just before its landing on Phobos surface. This paper reports the development and characterization of the deuterated PET.

Shifted excitation Raman difference spectroscopy: A promising tool for the investigation of soil

AbstractIn this paper we demonstrate shifted excitation Raman difference spectroscopy (SERDS) for soil analysis as a proof of concept. Confocal Raman microscopy is performed for sample analysis as well as for qualitative comparison with our SERDS experiments. Raman spectra of a soil sample show huge background signals, which mask weak Raman peaks. SERDS clearly separates the Raman signals from background signals with a 10‐fold improvement of the signal‐to‐background noise ratio. Thus, besides hydroxyapatite, additional Raman bands from quartz and feldspar could be extracted. The results demonstrate SERDS as a promising tool for soil analysis.Highlights Raman spectroscopy for soil characterization, e.g., for nutrient management. SERDS as a proof of concept for soil analysis. SERDS extracts Raman signals from disturbing background signals. SERDS as a promising tool for soil investigations.

Solubility and speciation of iron in hydrothermal fluids

Abstract Iron is among the most abundant elements in Earth's crust and is also a major aqueous solute in a variety of hydrothermal settings, yet major questions remain regarding the solubility and speciation of iron at hydrothermal conditions. Here, we conducted hydrothermal diamond-anvil cell experiments using synchrotron-radiation micro-XRF and XANES analyses as well as Raman spectroscopy, in situ at hydrothermal temperatures and pressures, to characterize the solubility and speciation of iron in fluids buffered by a variety of mineral assemblages. Our experiments included the assemblages hematite-magnetite (HM), fayalite-magnetite-quartz (FMQ), and magnetite-pyrite-pyrrhotite (MPP). Our results indicate highest solubilities of HM in HCl solutions. In sodium chloride solutions of similar molalities, FMQ shows higher Fe solubility than MPP. XANES data are interpreted as preponderance of ferrous iron in all experiments. Comparison of XANES spectra of these solutions with calculated XANES spectra from the literature indicates octahedral FeClx(H2O)6−x2−x (x = 0–3) as predominant Fe(II) species at lower Cl-Fe ratios, and suggests additional tetrahedral FeCl42− or FeCl3(H2O)− at high Cl-Fe ratios. Raman spectra to 600 °C show that the predominant species in ferric iron solutions is FeCl2(H2O)4+ at temperatures less than 100 °C, which transitions to FeCl4− between 100 and 200 °C. An additional Raman band that occurred in some spectra of a H2O + HCl fluid equilibrated with hematite ± magnetite at temperatures greater than 300 °C may originate from an FeCl3(H2O)x (x = 0–3) species. All Raman spectra of ferrous iron solutions show a fairly broad band at about 280 cm−1, which can be interpreted to stem from Fe(II)–Cl vibrations of FeCl3(H2O)x− (x = 0–3) (point group D3h) species or, at low Cl-Fe ratios of about two or less, from octahedral FeClx(H2O)6−x2−x (x = 0–3) species. These results provide important constraints on the hydrothermal mobilization of iron and fluid-rock reactions involving iron- and chloride-bearing fluids.

First-principles calculations and Raman scattering evidence for local symmetry lowering in rhombohedral ilmenite: temperature- and pressure-dependent studies

ATiO3-type materials may exist in two different crystalline forms: the perovskite and ilmenite. While many papers have devoted their attention to evaluating the structural properties of the perovskite phase, the structural stability of the ilmenite one still remains unsolved. Here, we present our results based on the lattice dynamics and first-principles calculations (density functional theory) of the CdTiO3 ilmenite phase, which are confronted with experimental data obtained through micro Raman spectroscopy that is a very good tool to probe the local crystal structure. Additional Raman bands, which are not foreseen from group-theory for the ilmenite rhombohedral structure, appeared in both low temperature (under vacuum condition) and high-pressure (at room temperature) spectra. The behavior can be explained by considering the local loss of inversion symmetry operation which reduces the overall space group from () to (). Our results can also be extended to other ilmenite-type compositions.

New minerals with a modular structure derived from hatrurite from the pyrometamorphic Hatrurim Complex. Part II. Zadovite, BaCa6[(SiO4)(PO4)](PO4)2F and aradite, BaCa6[(SiO4)(VO4)](VO4)2F, from paralavas of the Hatrurim Basin, Negev Desert, Israel

AbstractZadovite, BaCa6[(SiO4)(PO4)](PO4)2F (R3m, a = 7.0966(1) Å, c = 25.7284(3), V = 1122.13(3) Å3, Z = 3) and aradite, BaCa6[(SiO4)(VO4)] (VO4)2F (R3m, a = 7.1300(1), c = 26.2033(9) Å, V = 1153.63(6) Å3, Z = 3) are two new mineral species of a novel modular structure type related closely to the structure of nabimusaite, KCa12(SiO4)4(SO4)2O2F. Both minerals occur in paralavas enclosed in pyrometamorphic rocks of the Hatrurim Complex, Negev desert, Israel. Zadovite and aradite are colourless, transparent with a white streak, have a vitreous lustre and an uneven fracture. Both minerals are uniaxial (–) with refractive indices (589 nm) ω = 1.711(2), ε = 1.708(2) (zadovite) and ω = 1.784(3), ε = 1.780(3) (aradite). The zadovite structure type comprises two tetrahedral sites, which may host a broad compositional range of atoms such as Si, P, V and S. Results of electron microprobe analyses show a correlation between excess Si4+ and S6+ contents, suggesting the substitution scheme 2(P,V)5+ = Si4+ + S6+ at the tetrahedral sites. This points to the possibility of new minerals isostructural with zadovite with end-member formulae BaCa6(SiO4)2[(PO4)(SO4)]F, BaCa6(SiO4)2[(VO4)(SO4)]F, BaCa6[(SiO4)1.5(SO4)0.5](PO4)2F and BaCa6[(SiO4)1.5(SO4)0.5](VO4)2F. The Raman spectra of aradite and zadovite reflect the varying PO4 (e.g. change of band intensity at ∼1031 cm–1) and VO4 contents (e.g. change of band intensity at ∼835 cm–1). The presence of SO4 leads to an additional Raman band at ∼997 cm–1. The structure of zadovite-series minerals belonging to the nabimusaite group is characterized by a 1:1 alternation of antiperovskite-like {[FCa6](TO4)2}4+ modules and Ba(TO4)2–4 modules.

Lowering of stimulated Raman scattering threshold as a result of light capture

Stimulated Raman Scattering in globular photonic crystals and globular photonic glasses at different diameters of globules (250 – 400 nm) with embedded molecular liquids is studied under excitation by nanosecond or picoseconds laser pulses. Substantial decrease of Stimulated Raman Scattering threshold was observed. Such phenomenon was explained as the result of laser radiation field increase in globular photonic structures due to photonic density of states enhancement near the edges of photonic stop bands of photonic crystals and due to Mie resonance or whispering gallery modes effect revealing in photonic glasses. Stimulated Raman Scattering threshold lowering as a result of light capture in globular photonic crystals and photonic glasses opens the way to new efficient laser sources created on the base of composite globular photonic structures. Experimental data on spectra of Stimulated Raman Scattering in light and heavy waters are presented. As sources of exciting light the powerful ultra short solid state laser pulses with 532.0 nm wavelength and giant pulses of Ruby laser (694.3 nm) have been used. Several Stokes and anti-Stokes satellites were observed. Libration modes have been excited and resulted in some additional Raman bands at low frequency region and also as combining tones.

Compositional behavior of Raman-active phonons inPb(Zr1−xTix)O3ceramics

A systematic study of the Raman spectra of Pb(Zr1-xTix)O-3 (PZT) ceramics has been performed in a broad temperature interval (10-600 K) and a broad Ti/Zr concentration range around the morphotropic phase boundary (x = 0.25-0.70). The number of the spectral components was estimated by a standard fitting procedure with damped harmonic oscillators as well as by counting the number of peaks and shoulders with the help of a purposely designed mathematical analysis based on frequency derivatives of the Raman spectra. This last method proves to be very useful to study Raman spectra of disordered materials. For the case of PZT, the comparison with the Raman modes of PbTiO3 allows us to assign the phonon bands on both sides of the morphotropic phase boundary, and the crossover from the tetragonal to rhombohedral phase spectra is clearly visible. However, there are no indications of a systematic splitting of the E-symmetry modes into monoclinic A'-A '' doublets in the morphotropic samples. Detailed adjusting of the response function to the spectrum requires to assume additional Raman-active modes, but this holds for a much broader concentration range than that of the anticipated monoclinic phase. In particular, the lowest frequency transverse optic mode of E-symmetry (soft mode of the ferroelectric phase transition) is split into two components, a THz frequency anharmonic (central modelike) component and a resonant component (at omega similar to 80 cm(-1)), both related to the same normal coordinate. The additional Raman band appearing in this frequency range (omega similar to 65 cm(-1)) at low temperatures is rather associated with the antiphase tilt vibrations of the oxygen octahedra.

Abnormal elastic and vibrational behaviors of magnetite at high pressures.

Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature.

A vibrational spectroscopic study of the borate mineral takedaite Ca3(BO3)2

We have studied the mineral takedaite Ca3(BO3)2, a borate mineral of calcium using SEM with EDX and vibrational spectroscopy. Chemical analysis shows a homogeneous phase, composed of Ca. Boron was not detected. A very intense Raman band at 1087cm−1 is assigned to the BO stretching vibration of BO3 units. Additional Raman bands may be due to isotopic splitting. In the infrared spectrum, bands at 1218cm−1 and at 1163, 1262 and 1295cm−1 are assigned to the trigonal borate stretching modes. Raman bands at 712 and 715cm−1 are assigned to the in-plane bending modes of the BO3 units. Vibrational spectroscopy enables aspects of the molecular structure of takedaite to be assessed.

Evolution of Barnett Shale organic carbon structure and nanostructure with increasing maturation

The organic nanopore network of shales is believed to be the location of hydrocarbon trapping in source rocks. Better understanding of organic carbon structure and nanostructure constitutes a key point for estimating the oil and gas in-place at the local and basinal scale. Here we characterize, a maturation series from Mississippian Barnett Shale at multiple scales down to the nanometer scale. Organic petrography, Rock–Eval pyrolysis and Raman microspectroscopy are used to determine the organic matter properties (e.g. maturity, type, TOC content). Organic pore network attributes (e.g. pore size distribution, surface area, polyaromatic layers characteristics) are estimated using low pressure gas adsorption analyses and direct imaging by high-resolution transmission electron microscopy (HRTEM). Based on Raman data we show that Barnett Shale organic matter has only reached the level of carbonization, even within overmature samples; graphitization has not yet been triggered. Interestingly, the investigated samples exhibit an additional broad Raman band centered at about 1480cm−1, likely due to the presence of retained hydrocarbons within the organic matter nanoporosity. Low pressure gas adsorption analyses evidence a positive correlation between surface areas, mesopores (pores of about 2–50nm of diameter) and maturity level. HRTEM images confirm Raman data: even the overmature organic matter remains disordered. Such disorientation of nanometer sized polyaromatic layers creates a nanoporosity network in organic matter that appears most developed in samples of gas window maturity. Furthermore, carbon nanoparticles of concentric nanostructures, known to result from the thermal cracking of hydrocarbons, are detected in overmature samples.

Peroxide-doped apatites: Preparation and effect of synthesis parameters

This contribution focused on the preparation of peroxide-doped calcium phosphate apatites — in view of potential uses as bioactive bioceramics with antimicrobial functions, and on their main physico-chemical characteristics. Two synthesis routes were investigated. First, the hydrolysis of β-TCP in the presence of H2O2 was followed. However, only elevated concentrations in H2O2 in the medium or temperatures around 150°C allowed us to reach the complete β-TCP-to-apatite hydrolysis process, and the obtained samples exhibited a high crystallinity state with no non-apatitic chemical environments. The second protocol tested consisted in the direct apatite precipitation in the presence of H2O2 in the medium (at room temperature). This protocol led to single-phased nanocrystalline apatites, and our data indicate that part of the apatitic OH− ions were substituted by oxygenated species, and typically by peroxide ions (quantified). Physico-chemical modifications in the form of an improvement in crystallinity state, an increase in unit cell volume, and the presence of additional Raman bands were noticed and discussed.

Infrared and Raman spectroscopic characterization of the carbonate mineral huanghoite – And in comparison with selected rare earth carbonates

Raman spectroscopy complimented with infrared spectroscopy has been used to study the rare earth based mineral huanghoite with possible formula given as BaCe(CO3)2F and compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of huanghoite displays three bands are at 1072, 1084 and 1091cm−1 attributed to the CO32- symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of CO32- symmetric stretching vibration varies with mineral composition. Infrared spectroscopy of huanghoite show bands at 1319, 1382, 1422 and 1470cm−1. No Raman bands of huanghoite were observed in these positions. Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554cm−1 assigned to the ν3 (CO3)2− antisymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands for huanghoite are observed at 687, 704, 718 and 730cm−1and assigned to the (CO3)2− ν2 bending modes. Raman bands are observed for huanghoite at around 627cm−1 and are assigned to the (CO3)2− ν4 bending modes. Raman bands are observed for the carbonate ν4 in phase bending modes at 722cm−1 for bastnasite, 736 and 684cm−1 for parisite, 714cm−1 for northupite. Raman bands for huanghoite observed at 3259, 3484 and 3589cm−1 are attributed to water stretching bands. Multiple bands are observed in the OH stretching region for bastnasite and parisite indicating the presence of water and OH units in their mineral structure. Vibrational spectroscopy enables new information on the structure of huanghoite to be assessed.

Infrared and Raman spectroscopic characterization of the carbonate mineral weloganite – Sr3Na2Zr(CO3)6·3H2O and in comparison with selected carbonates

The mineral weloganite Na2Sr3Zr(CO3)6·3H2O has been studied by using vibrational spectroscopy and a comparison is made with the spectra of weloganite with other carbonate minerals. Weloganite is member of the mckelveyite group that includes donnayite-(Y) and mckelveyite-(Y).The Raman spectrum of weloganite is characterized by an intense band at 1082cm−1 with shoulder bands at 1061 and 1073cm−1, attributed to the CO32- symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of CO32- symmetric stretching vibration varies with mineral composition. The Raman bands at 1350, 1371, 1385, 1417, 1526, 1546, and 1563cm−1 are assigned to the ν3 (CO3)2− antisymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for weloganite is significant in that it shows distortion of the carbonate anion in the mineral structure. The Raman band observed at 870cm−1 is assigned to the (CO3)2− ν2 bending mode. Raman bands observed for weloganite at 679, 682, 696, 728, 736, 749, and 762cm−1 are assigned to the (CO3)2− ν4 bending modes. A comparison of the vibrational spectra is made with that of the rare earth carbonates decrespignyite, bastnasite, hydroxybastnasite, parisite, and northupite.

Preparation and characterization of nanocrystalline Ca-doped CeO2 by sol–gel process

The reactivity of CeO2 is determined by grain size and oxygen vacancies, which can be achieved by doping elements with less oxidation state into CeO2. In this study nanocrystalline Ca-doped CeO2 sol was synthesized from the reaction of hydrate cerium (III) nitrate and calcium nitrate tetrahydrate in alcohol solution after being calcined at 600 °C. X-ray diffraction as well as selected area electron diffraction gave evidence that the synthesized Ca-doped CeO2 samples were well crystalline and had a cubic fluorite structure. TEM observation revealed that Ca-doped CeO2 was composed by nanoparticles with grain size around 8 nm. The Raman spectrum of pure CeO2 consists of a single triple degenerate F2g model characteristic of the fluorite-like structure. In the Ca-doped CeO2 sample, two additional low-intensity Raman bands were detected, thus confirming the formation of the solid solution. The synthesized nanometric powder is expected to be used in solid oxide fuel cells as well as in the catalytic treatment of automobile exhaust fumes.

Temperature-dependent Raman scattering study of the defect pyrochlores RbNbWO6 and CsTaWO6

Lattice dynamics calculations and temperature-dependent Raman scattering experiments were performed on RbNbWO6 and CsTaWO6 pyrochlore oxides. The observed bands were assigned to the respective motions of atoms in the unit cell. The spectra showed the presence of additional Raman bands not allowed for by the cubic structure. We have shown that these bands appear due to both substitutional disorder in the 16c sites and displacive disorder of the A ions. Raman studies also revealed the presence of an additional 80 cm−1 band at room temperature for RbNbWO6, not observed for CsTaWO6. The presence of this band has been attributed to off-center displacement of the Nb and W ions due to structural phase transition into a tetragonal ferroelectric phase. The temperature evolution of the 80 cm−1 band intensity revealed that it disappeared at a much higher temperature (about 650 K) than the reported phase transition temperature (about 360 K). This behavior is reminiscent of chemically disordered perovskite ferroelectrics, including relaxor ferroelectrics, and was attributed to the presence of small polar regions with local tetragonal distortion embedded in the paraelectric matrix of the structure.

Raman spectrum of decrespignyite [(Y,REE)4Cu(CO3)4Cl(OH)5·2H2O] and its relation with those of other halogenated carbonates including bastnasite, hydroxybastnasite, parisite and northupite

AbstractRaman spectroscopy complemented with infrared spectroscopy has been used to study the rare‐earth‐based mineral decrespignyite [(Y,REE)4Cu(CO3)4Cl(OH)5· 2H2O] and the spectrum compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of decrespignyite displays three bands at 1056, 1070 and 1088 cm−1 attributed to the CO32− symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of the CO32− symmetric stretching vibration varies with the mineral composition. The Raman spectrum of decrespignyite shows bands at 1391, 1414, 1489 and 1547 cm−1, whereas the Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554 cm−1, respectively, assigned to the ν3 (CO3)2− antisymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands are observed at 791, 815, 837 and 849 cm−1, which are assigned to the (CO3)2−ν2 bending modes. Raman bands are observed for decrespignyite at 694, 718 and 746 cm−1 and are assigned to the (CO3)2−ν4 bending modes. Raman bands are observed for the carbonate ν4 in‐phase bending modes at 722 cm−1 for bastnasite, 736 and 684 cm−1 for parisite and 714 cm−1 for northupite. Multiple bands are observed in the OH stretching region for decrespignyite, bastnasite and parisite, indicating the presence of water and OH units in the mineral structure. Copyright © 2011 John Wiley & Sons, Ltd.

Micro‐Raman investigation of terra sigillata slips: a comparative study of central Italian and southern Gaul productions

AbstractTerra sigillata is certainly the most famous fine ware of the Roman period, and for this reason it has been a subject of interest for both the archeology and archeometry communities. X‐ray diffraction studies showed systematic differences in the mineral compositions between central Italian and south Gaul productions. All the slips contain hematite; the Gallic ones embody also a significant content of corundum, while the Italian productions contain a great proportion of spinel. Raman investigation fails to reveal directly these differences because the spectra are dominated by the hematite peaks. However, we originally demonstrate that, due to the occurrence of an upshift of bands, the Raman spectrum of these sigillata slips can be associated with a substituted hematite. This premise has been confirmed by comparing the crystallization of hematite in four annealed clays to that of the ancient slips. The results suggested that the presence of the strong additional Raman band at around 680 cm−1 present in both clays and ancient slips could be associated with the recrystallization of hematite, occurring above 750 °C. It could also be due to the magnetite content, but this hypothesis is not supported by X‐ray diffraction data. In addition, the reduction seems to take place only above 1050 °C, as suggested by the unveiling of hercynite as well as the darkening of the clay samples. Raman scattering is shown to be very sensitive to small variations in clays composition and to firing temperature, and it has been successfully used as an in situ sensitive probe for discriminating between Italian and south Gallic productions. Copyright © 2010 John Wiley & Sons, Ltd.

Synthesis and Raman Scattering from Zn1−x MnxS Diluted Magnetic Semiconductor Nanowires

The growth of Diluted Magnetic Semiconducting (DMS) Zn(1-x)Mn(x)S (0 < or = x < 0.6) nanowires (NWs) using a three-zone furnace and two solid sources is reported. The approach is generally applicable to many binary and ternary NW systems that grow by the Vapor-Liquid-Solid growth mechanism. Mn concentration was controlled by the temperature of the Mn source. The Zn/Mn ratio was found to determine the crystalline structure, i.e., wurtzite or zinc blende. High-resolution transmission electron microscopy measurements revealed highly crystalline single phase NWs. The vibrational properties of the DMS NWs with different Zn/Mn ratios were studied by correlating their Raman scattering spectra with the composition measured by Energy Dispersive X-Ray Spectroscopy (EDS). We find that the transverse optical (TO) phonon band disappears at the lowest Mn concentrations, while the longitudinal optical (LO) phonon band position was found insensitive to x. Three additional Raman bands were observed between the ZnS q = 0 TO and LO phonons when Mn atoms were present in the NWs. These bands are similar to those reported previously for bulk Zn(1-x)Mn(x)S and their origin is still controversial.