bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐pressure metastable phase transitions in β‐Ge3N4 studied by Raman spectroscopy
Authors: McMillan Paul F. , Deb Sudip K. , Dong Jian‐Jung 
Published: August 2003

AbstractWe studied polymorphic transitions occurring in β‐Ge3N4 metastably compressed to high pressures (P = 40 GPa) at room temperature. Previous studies under high‐pressure–high‐temperature conditions have shown that this phase transforms into a newly discovered spinel‐structured material (γ‐Ge3N4) above 10 GPa and 1200°C. However, ab initio theoretical studies have indicated that the phenacite‐structured low‐pressure β‐Ge3N4 polymorph should also undergo a series of metastable transformations upon compression at low temperatures. Here we studied these transformations by in situ Raman spectroscopy in a diamond anvil cell. The phase transitions were first predicted to involve a sequence of second‐order phase changes driven by soft phonon modes at the Brillouin zone centre (the Γ point: q = 0) resulting in displacive motions of the N atoms, causing the symmetry to descend from P63/m through P6 to P3. The two transitions were predicted to occur at P = 20 and 28 GPa. However, it was also noted that a direct first‐order transition between P63/m and P3 phases might occur at P = 23 GPa if order–disorder processes or phonon condensations away from the Brillouin zone centre were considered. Here we present experimental evidence for a phase transition occurring at P = 20 GPa, within β‐Ge3N4 that has been metastably compressed at ambient temperature. From the number of Raman modes observed, this transition most likely corresponds to the direct P63/m–P3 transformation, and it is therefore first order in character, but with a small activation energy barrier as ascertained by little or no hysteresis observed upon decompression. However, when all the minor features appearing in the Raman spectrum are accounted for, the number of observed resonances is greater than the number of zone centre modes expected even for the P3 structure. This indicates that the true unit cell is larger than expected from zone‐centre mode softening, and that order–disorder processes or phonon instabilities at q≠0 must have occurred during the transition. Copyright © 2003 John Wiley & Sons, Ltd.
Raman scattering studies at high pressure and low temperature: technique and application to the piezoelectric material PbZr0.52Ti0.48O3
Authors: Haines J. , Rouquette J. , Bornand V. , Pintard M. , Papet Ph. , Gorelli F. A. 
Published: August 2003

AbstractRaman spectroscopy is a powerful tool for the study of solids under extreme conditions of pressure and temperature. This technique can be used to determine phase diagrams and study phase transition mechanisms. Raman spectroscopy can be used to characterize disorder present in crystalline solids and is sensitive to local structural configurations. The combined use of diamond anvil cells and closed‐cycle helium cryostats enables Raman scattering experiments to be performed at pressures exceeding 50 GPa in the 10–300 K temperature range. The use of this technique to study the perovskite‐type piezoelectric material PbZr0.52Ti0.48O3 enables the monoclinic and cubic phases present in this system to be characterized and their pressure–temperature domains of stability to be defined. Raman scattering results indicate the presence of polar domains in the cubic, high‐pressure phase. The ferroelectric monoclinic phases exhibit extended stability at high pressure and low temperature. Copyright © 2003 John Wiley & Sons, Ltd.
High‐pressure phase transitions in tetrahedrally coordinated chain structures
Authors: Serghiou G. 
Published: August 2003

AbstractWe present an overview of phase transition trends and medium range order structural criteria proposed to dictate the transformation of chain silicates to either dense crystalline or amorphous phases at high pressures. These are based on Raman spectroscopic measurements of the tetrahedrally coordinated (SiO4) chain silicates MgSiO3, Ca0.5Mg0.5SiO3, CaSiO3 and MnSiO3 and of octahedrally coordinated (SiO6) MgSiO3 ilmenite to 70 GPa. The tetrahedrally coordinated structures either become amorphous or transform to dense crystalline phases upon compression, depending on the sequencing of their building blocks (labeled P and C modules). Chain silicates containing only P modules transform to dense crystalline phases whereas chain silicates containing a sequence of P and C modules become amorphous, and those containing only C modules exhibit both crystalline and amorphous regions. Based on a comparison with the high‐pressure Raman spectra of octahedrally coordinated (SiO6) ilmenite MgSiO3, the dense metastable high pressure crystalline Ca0.5Mg0.5SiO3, MgSiO3 and CaSiO3 phases also contain SiO6 units. Copyright © 2003 John Wiley & Sons, Ltd.
In situ Raman monitoring of the growth of CVD diamond films
Authors: Mermoux M. , Marcus B. , Abello L. , Rosman N. , Lucazeau G. 
Published: August 2003

AbstractRaman spectroscopy was applied to monitor the growth of diamond in different plasma‐assisted chemical vapour deposition reactors. A gated, multichannel detection system was used to discriminate against the high level of background radiation produced by the plasma and the hot substrate. As a result, Raman spectra could be taken during diamond growth without interruption of the process. The ability to detect and distinguish between diamond and non‐diamond phases during film growth is demonstrated. A sufficient signal‐to‐noise ratio in the spectra was achieved for stress formation to be observed. Copyright © 2003 John Wiley & Sons, Ltd.
High temperatures and Raman scattering through pulsed spectroscopy and CCD detection
Authors: Simon P. , Moulin B. , Buixaderas E. , Raimboux N. , Herault E. , Chazallon B. , Cattey H. , Magneron N. , Oswalt J. , Hocrelle D. 
Published: August 2003

AbstractA Raman scattering system devoted to high temperatures is presented. It is based on a pulsed system to remove thermal emission with retaining charge‐coupled device (CCD) detection. Two types of optical gating are used: a Pockels switch or an intensified CCD (ICCD), combining in this case the optical gate and the CCD detection. The performances of both systems are presented and their respective advantages are discussed and compared. The ICCD device allows recording of spectra in the 2000°C range, and typical results obtained on alumina and zirconia ceramics are shown. Copyright © 2003 John Wiley & Sons, Ltd.
High‐pressure polymerization of phenylacetylene and of the benzene and acetylene moieties
Authors: Santoro Mario , Ciabini Lucia , Bini Roberto , Schettino Vincenzo 
Published: August 2003

AbstractThe reactivity induced in acetylene, benzene and phenylacetylene crystals by the application of high external pressure is discussed. Acetylene, the simplest model system involving the CC triple bond, reacts above 3.0 GPa in the orthorhombic crystal phase. The molecular arrangement in this phase determines the final conformation of the recovered polymer. The role of laser irradiation in branching the polyenic chains, through the dissociation of the double bonds, is revealed. Benzene, the model aromatic molecule, starts to react in the solid state above 23 GPa. A progressive distortion of the rings is observed on increasing pressure up to 50 GPa but the transformation becomes complete, close to ambient pressure, only during the decompression run. An amorphous hydrogenated carbon compound (a‐C:H) is formed in this reaction. Laser irradiation with suitable wavelengths reduces the reaction pressure threshold revealing the role of the S1 excited state in driving the high‐pressure reaction. Finally, phenylacetylene was taken into account since it is the simplest molecule involving both the triple bond and the aromatic ring and its reactivity could be possibly interpreted according to the previous model systems. Phenylacetylene starts to react in the solid state above 8 GPa. The reaction mainly involves the triple bond of the ethynyl fragment forming polyphenylacetylenic chains. On the basis of the infrared spectra a possible polymer structure is proposed. Copyright © 2003 John Wiley & Sons, Ltd.
Effect of pressure and temperature on Raman spectra of solids: anharmonicity
Authors: Lucazeau Guy 
Published: August 2003

AbstractThis paper gives a brief review of the effect of temperature and pressure on Raman spectra. Anharmonicity, defined by the cubic, quartic and higher terms in the potential expansion, is shown to be responsible for various properties such as dilatation or for variations of wavenumber and half‐width of Raman bands with temperature and pressure, or may be strongly involved in phase transitions. This contribution does not pretend to be an exhaustive review on the subject but aims to introduce some basic concepts in a tutorial way before showing how intricated are these manifestations of anharmonicity. Copyright © 2003 John Wiley & Sons, Ltd.
Raman spectroscopy of metals, high‐temperature superconductors and related materials under high pressure
Authors: Goncharov Alexander F. , Struzhkin Viktor V. 
Published: August 2003

AbstractAn overview is presented of recent Raman scattering measurements in metals under conditions of high static pressure in the diamond anvil cell. Also discussed are the practical improvements of the traditional technique that have made these measurements possible. We present the results of several studies including those of hexagonal close‐packed (hcp) ε‐Fe and its solid solutions Fe(1−x)Nix (x ≤ 0.2) over a wide temperature range, and also of high‐temperature superconductors (YBCO) and their prototypes, i.e. materials with strong electronic correlations such as the 3d metal oxides CoO and FeO. Copyright © 2003 John Wiley & Sons, Ltd.
Brillouin scattering at high pressure: an overview
Authors: Polian Alain 
Published: August 2003

AbstractBrillouin scattering allows the determination of acoustic velocities and adiabatic elastic moduli in matter. These data are crucial in many areas of science, such as fundamental physics, geosciences and technology, especially when measured as a function of the density (pressure). In this paper, we present a review of the work performed on Brillouin scattering under high pressure in diamond anvil cells, emphasizing the most recent results. Copyright © 2003 John Wiley & Sons, Ltd.
High‐pressure Raman spectroscopy of nano‐structured ABO3 perovskites: a case study of relaxor ferroelectrics
Authors: Kreisel J. , Bouvier P. 
Published: August 2003

AbstractA large number of outstanding physical properties observed in perovskite‐type oxides, such as giant piezoelectricity, colossal magneto‐resistance and high‐Tc superconductivity, are related to an intrinsic nano‐scaled local structure. For instance, the presence of a nano‐scaled structure is characteristic of so‐called relaxor ferroelectrics (relaxors), which have attracted considerable attention since the recent discovery of ultra‐high strain and giant piezoelectric properties. In this paper we review, through a case study of relaxors, how the combination of the external parameter high‐pressure and Raman spectroscopy allows an instructive investigation of nano‐scaled perovskites, which is often at best a difficult task for conventional ‘average‐structure’ techniques such as diffraction. We show that perovskite‐type relaxors present important pressure instabilities with respect to both cation sizes and we suggest that the latter instabilities might well be at the origin of the reduced dielectric performances that are observed for strained thin‐film relaxors. Finally, we briefly illustrate how the approach might be used for nano‐scaled manganite‐type oxides. Copyright © 2003 John Wiley & Sons, Ltd.
Raman spectroscopy as a probe for in situ studies of pressure‐induced amorphization: some illustrative examples
Authors: Pereira A. S. , Perottoni C. A. , da Jornada J. A. H. 
Published: August 2003

AbstractThe main models proposed in the literature to describe pressure‐induced amorphization (PIA) are briefly reviewed, with special emphasis on the kinetic aspects of PIA. The high potential of Raman spectroscopy for experimental studies on PIA is highlighted and illustrated by the results obtained for zirconium tungstate (ZrW2O8) and boric acid (H3BO3). Compared with x‐ray diffraction using a conventional x‐ray tube, Raman spectroscopy allowed a much faster identification of the transitions in both compounds. Further, the Raman results for ZrW2O8 have given support to an amorphization mechanism based on the freezing of low‐energy vibrational modes associated with rigid (or quasi‐rigid) ZrO6 and WO4 polyhedral units. For H3BO3, we obtained strong evidence of a PIA associated with hindered decomposition of H3BO3, probably to a mixture of HBO2 and H2O. The short acquisition time for the Raman measurements of samples under high pressure enabled us to follow the kinetics of the transition on H3BO3, which could hardly be done by conventional x‐ray diffraction. Raman spectroscopy proved to be a very convenient technique to study the mechanisms behind PIA, owing not only to the fast acquisition of information about phase transition kinetics, but also to the structural information that can be obtained. Copyright © 2003 John Wiley & Sons, Ltd.
Raman spectroscopy on carbon nanotubes at high pressure
Authors: Loa I. 
Published: August 2003

AbstractRaman spectroscopy has been the most extensively employed method to study carbon nanotubes at high pressures. This review covers reversible pressure‐induced changes of the lattice dynamics and structure of single‐ and multi‐wall carbon nanotubes and irreversible transformations induced by high pressures. The interplay of covalent and van der Waals bonding in single‐wall nanotube bundles and a structural distortion near 2 GPa are discussed in detail. Attempts to transform carbon nanotubes into diamond and other ‘superhard’ phases are reviewed critically. Copyright © 2003 John Wiley & Sons, Ltd.
Phase diagram of ice in the VII–VIII–X domain. Vibrational and structural data for strongly compressed ice VIII
Authors: Pruzan Ph. , Chervin J. C. , Wolanin E. , Canny B. , Gauthier M. , Hanfland M. 
Published: August 2003

AbstractThe first part of this paper presents a short survey on the phase diagram of ice in the pressure range from 2 to 100 GPa from 10 to 300 K. The description is mainly devoted to the problem of the symmetrization of the O—H· · ·O bond, that is, the transformation of ice VII or VIII to ice X. In connection with this introduction, in the second part of the paper new vibrational and structural data obtained from Raman scattering and x‐ray diffraction in ice VIII are given and these properties are compared with those of ice VII. Specifically, below 100 K, solid VIII vanishes at 62 GPa to give birth to a state which is the first step to ice X. This transition is marked by a softening of the lowest Raman‐active lattice mode and the disappearance of the Raman signal. During the compression of ice VIII the O–H stretching mode wavenumber shows soft mode behaviour. It is found that the expansivity of ice VIII is negative above 10 GPa. Copyright © 2003 John Wiley & Sons, Ltd.
High‐pressure antiferromagnetic phases of solid oxygen
Authors: Gorelli F. A. , Santoro M. 
Published: August 2003

AbstractWe report on the antiferromagnetic character of solid oxygen in the high‐pressure, low‐temperature region enclosed between the β and ε phases. The occurrence of a first‐order phase transition, positioned at 5.5–6.5 GPa, between the monoclinic α (C2/m) and the orthorhombic δ (Fmmm) phases was shown by means of an accurate x‐ray diffraction analysis. The two crystal structures were assessed to be antiferromagnetically ordered, owing to a narrow peak observed in the IR spectrum and assigned to a vibron component. The absorption of this mode is allowed owing to the coupling of the molecular spins, which produces a doubling of the primitive cell. The vibrational coupling parameter was quantitatively related to the exchange integralJinvolved in the Heisenberg interaction. Finally, absorption measurements at different pressures of the electronic transition$^{3}\Sigma_{g}^{-} \rightarrow{}^{1}\Delta_{g}$, lying in the near‐IR spectral range, allowed us, by means of a simple model, to obtain directly the quantityJas a function of the nearest‐neighbour distance. Copyright © 2003 John Wiley & Sons, Ltd.
Megabar high‐pressure cells for Raman measurements
Authors: Eremets M. I. 
Published: August 2003

AbstractExperimental aspects of Raman measurements at megabar pressures are considered. Features of diamond anvil cells working above 200 GPa are described. Problems of luminescence background at megabar pressures and the use of low‐luminescence diamonds are considered. Methods of pressure measurements at very high pressures are discussed. The pressure dependence of the Raman shift from the diamond anvil tip was used as a reliable estimate of the pressure. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of alkaloids in Ipecacuanhae radix and preparations by capillary zone electrophoresis
Authors: Sturm Sonja , Taglioli Vania , Bilia Anna R. , Vincieri Francesco , Stuppner Hermann 
Published: August 2003

AbstractA capillary zone electrophoresis method for quantitation of the alkaloids emetine and cephaeline in Ipecacuanhae radix fluid extract and Ipecac syrup using papaverine as internal standard is described. Baseline separation was achieved within 10 min using a fused silica capillary and a running electrolyte consisting of citric acid (50 mM), disodium hydrogenphosphate (100 mM), and 2.5% methanol (pH 4.4). Regression equations revealed a linear response from 0.05 to 1.9 mg/mL for cephaeline and emetine (correlation coefficients 0.9991–0.9993). The lowest quantitation limits were determined as 0.03 mg/mL for both alkaloids, and the limit of detection was 0.012 mg/mL. The day‐to‐day variations of retention times were < 1.3% for both compounds. Whereas no sample pre‐treatment was necessary for analysis of the fluid extract, SPE had to be applied before CE analysis of the syrup. The recovery rate for emetine in this case was > 99.8%.
Study on the feasibility of coupling large‐volume injection to fast gas chromatography with mass spectrometric detection for analysis of organochlorine pesticides
Authors: Korenková Eva , Matisová Eva , Slobodník Jaroslav 
Published: August 2003

AbstractA combined use of programmable temperature vaporisation injector, fast oven temperature ramp, 0.1 mm ID analytical column and hydrogen carrier gas enabled injection of up to 20 μL of extract containing 15 organochlorine pesticides and separation of all analytes in less than 8 minutes.
Comprehensive two‐dimensional gas chromatography (GC×GC) and GC×GC‐quadrupole MS analysis of Asian and American ginseng
Authors: Shellie Robert A. , Marriott Philip J. , Huie Carmen W. 
Published: August 2003

AbstractExtracts of the roots of Panax (ginseng) species are analysed using comprehensive two‐dimensional gas chromatography. Comparison of comprehensive two‐dimensional chromatograms reveals the presence of numerous common components, and possible species‐specific components are also observed. Two‐dimensional bubble plot presentations of GC×GC(FID) data allow ready qualitative and semi‐quantitative comparison of the extracts. The use of GC×GC‐quadrupole MS (GC×GC‐qMS), operated at a scanning rate of 20 Hz, in conjunction with retention data, permits identification of separated (major) components. Whilst this scan speed will be insufficient for reliable quantitative analysis, considerably improved quality of uncorrected spectra, arising from the enhanced separation over single column GC‐MS analysis is apparent. Spectral match qualities of up to 99% are found for a number of components. Comparison of GC×GC‐qMS with GC×GC(FID) indicates that good correspondence of peak position patterns is achieved, which aids component identification. It is shown that (quadrupole) mass spectrometric detection is a useful tool for provision of identification of separated compounds in high‐resolution comprehensive two‐dimensional gas chromatography.
Analysis of plasma catecholamines by liquid chromatography with amperometric detection using a novel SPE ion‐exchange procedure
Authors: Raggi Maria Augusta , Sabbioni Cesare , Nicoletta Gianluca , Mandrioli Roberto , Gerra Gilberto 
Published: August 2003

AbstractSimultaneous determination of the three main catecholamines (Epinephrine, Norepinephrine, and Dopamine) has been implemented by means of liquid chromatography with amperometric detector working in oxidation at +800 mV. The chromatographic analysis was carried out on a reversed phase column (C8 Rainin 150×4.6 mm ID, 5 μm) with a mixture of methanol and an aqueous solution of 5 mM of citric acid, 20 mg L–1 octanesulfonic acid, and 20 mg L–1 EDTA (pH 2.9) as the mobile phase. An original solid phase extraction pretreatment of plasma samples was developed using cationic ionic exchange cartridges with carboxypropylic adsorbent. The steps of the SPE procedure were carefully checked and optimal elution was carried out with perchloric acid. High extraction yield values were obtained for all catecholamines with good reproducibility. Linearity was observed in the 0.06–3.00 ng mL–1 concentration range for all analytes. LOD and LOQ were respectively 0.03 ng mL–1 and 0.06 ng mL–1. The method was applied successfully to the analysis of some real plasma samples from young volunteers under experimental psychological stress.
Study of electroosmotic flow profile by processing of virtual digital Shah function mask and Fourier transform
Authors: Kitagawa Shinya , Mitsuya Kotaro , Chaiyasut Chaiyavat , Tsuda Takao 
Published: August 2003

AbstractThe electroosmotic flow in a packed capillary column (CEC) and in a rectangular capillary (CE) was observed by using a microscope‐CCD‐camera system. The observed image was captured to PC, and virtual digital Shah function mask processing was applied. The flow velocity was calculated by Fourier transform methods. The flow profile was analyzed by multiple measurements of the flow velocity in adjoining regions. The velocity of the electroosmotic flow in a packed capillary column (ID 150 μm, length 18 mm, packed with cation exchanger) was 4.49 μm/s at any point of the column, and the flow profile was flat. The effect of gravity on electroosmotic flow was also studied. The profile of the electroosmotic flow was almost flat under both 1‐G and microgravity, and the electroosmotic flow velocity under microgravity was found to be significantly faster than that under 1‐G.