Results 1 - 10 of 1355
Results 1 - 10 of 1355. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] We present a new method for improving the reliability of quantitative analysis by laser-induced breakdown spectroscopy (LIBS). The method can be considered as a variation of the calibration-free LIBS approach; although not completely standard-less, only one standard of known composition and similar matrix to the one to be analyzed is needed. On the other hand, the one-point calibration approach allows the empirical determination of essential experimental and spectroscopic parameters, whose knowledge is often imprecise or lacking; the result is a definite improvement of the trueness of LIBS analysis with respect to the traditional calibration-free approach. The characteristics and advantages of the proposed one-point calibration LIBS approach will be demonstrated on a set of copper-based samples of known composition. - Highlights: • A new method for improving the quantitative analysis by LIBS is presented. • Only one standard of known composition is needed for the analysis. • A set of copper-based samples of known composition is analyzed. • The concentrations calculated result remarkably close to the nominal concentrations
[en] Synthesis and sintering studies of ferroelectric ceramics of (Pb, Ba) Nb2 O6, or PBN, were performed by conventional method. The raw materials Ba (NO3)2 and Ba O were tested for the comparison of the homogeneity and the reactivity of the powders. The X-ray diffraction analysis showed that the material studied presents only the PBN phase and the raw material influences strongly the structure symmetry of the final product. The dielectric properties, obtained by impedance spectroscopy in function of temperature, were compared to those reported by literature in single crystals of same composition. (author)
[en] Research highlights: → The structure of In3TeO3F7 is based on the stacking of identical layers of InF6 and InO2F4 octahedra and InO4F3 pentagonal bipyramids. → It corresponds an intergrowth of parallel strips of MIn3F10 and hexagonal tungsten bronze (HTB)-types. → The Te+4 cations are located inside hexagonal tunnels and bonded to F anions located in the same tunnels. - Abstract: After InTeO3F and InTe2O5F recently described, a new compound In3TeO3F7 is characterized in the In-TeIV-O-F system. The crystal structure was determined by single X-ray diffraction and refined to R1 = 0.028. In3TeO3F7 crystallizes in orthorhombic space group Cmmm, a = 7.850(2) A, b = 27.637(6) A, c = 4.098(1) A, V = 889.1(4) A3 and Z = 4. Its structure consists of the stacking, via vertices, of identical layers composed of InF6 and InO2F4 octahedra sharing corners and of InO4F3 pentagonal bipyramids sharing edges and vertices. The Te cations statistically occupy one or the other of two close sites located inside tunnels delimited by the In polyhedra and are bonded to F anions located in the same tunnels. The structure can be considered as an intergrowth of parallel strips of MIn3F10 and hexagonal tungsten bronze (c)-types. It is compared to other structures such as the bronze Sb0.157WO3, TeMo5O16 and Sb2Mo10O31, phases also comprising Te4+ or Sb3+ inside hexagonal tunnels. The electronic lone pair of Te4+ is stereochemically active and a perfect O/F ordering occurs on the anionic sites.
[en] The ultrasonic spray pyrolysis technique has been, during last three decades, one of the major techniques of synthesis a wide variety of materials. One of the most important among the ionic conductors is lithium phosphorous doped tungsten bronze. The main goal of this investigation is producing full or hallows spheres of these bronzes of very narrow distribution. The mean size and size distribution specter of all materials were determined by the SEM analysis. The results were compared with the values obtained from the theoretical model. The assembled results indicate the possibility of a rigorous particle structure designing of all obtained powders
[en] Tungsten oxide thin films injected with protons (H xWO3) during deposition were prepared on glass substrates using reactive direct-current magnetron sputtering in a mixture of argon, oxygen, and hydrogen gases. The as-deposited films were bronze. The amount of injected protons, namely the x-value in H xWO3, was estimated using the dispersion of the extinction coefficient (κ). The dispersion was evaluated by analyzing the experimental spectra measured with spectroscopic ellipsometry and optical photometry using the model composed of a homogeneous tungsten bronze layer with an additional surface roughness layer. As a result of analysis, the x-value was estimated to be approximately 0.1
[en] Corrosion phenomena on copper and copper based alloys have been the subject of great interest because of the numerous use of these materials in structural, architectural, artistic, electrical and electronic devices. The first part of this thesis focuses on the activities within the IMMACO-Project (Improvement of Means of Measurement on Archaeological Copper Alloys for Characterization and Conservation) of the European Union. This project aims the production of certified reference materials (CRM) for the investigations of archaeological alloys. Within the scope of the second part of the presented thesis a new set-up of different techniques for in-situ investigations was applied to pure copper and bronze in order to obtain information about the initial stages of atmospheric corrosion. Atomic force microscopy (AFM) was used for the investigation of topographical changes of the surface upon exposure to a defined atmosphere. A combination of infrared reflection and adsorption spectroscopy (IRAS) and quartz crystal microbalance (QCM) delivered chemical and kinetic information about the corrosion process. The influence of humidity, SO2, O3, and NO2 to the corrosion behavior of pure copper is investigated. At 60 % relative humidity (RH) small cuprous oxide features partly covering the surface are observed, whereas a fast formation of a layer of cuprous oxide entirely covering the copper surface was obtained at 80 % RH. Copper exposed to humidified air with SO2 yielded in the formation of cuprous oxide as well as copper sulfite. A detailed investigation of the influence of O3 to the corrosion process of pure copper showed that copper sulfite is further oxidized to copper sulfate and the formation of cuprous oxide is promoted. NO2 enables also an oxidation of sulfite to sulfate, but not in the same extent as O3 and reduces the formation rate of cuprous oxide. In addition to the weathering experiments carried out on pure copper investigations by means of AFM and IRAS were also performed on samples of the CRMs of the IMMACO-Project. Some of these samples were also used for ex-situ investigations with X-ray photoelectron spectroscopy (XPS). In synthetic humidified air a slower weathering process was observed for the copper alloys than for pure copper, which is obviously caused by the formation of a protective Pb oxide layer. In SO2 containing humidified air the formation of large copper sulfite features was observed. Furthermore, the formation of cuprous oxide was detected 486 min after adding SO2 to the gas stream with IRAS. This fact and the decreased amount of Pb on the surface during the exposure in SO2 containing atmosphere gives evidence that the formed lead oxide layer has protective properties and must be destroyed before any surface reaction can occur between the bronze sample and the ambient atmosphere. (author)
[en] Ceramics of the tetragonal tungsten bronze type of structure (Srx Ba1-x) Nb2 O6 (SBN), with x=0.25, x=0.50 e x=0.75, were synthesized by conventional methods. The dielectric and pyroelectric properties were analyzed with intention to determine the potential of the SBN ceramics for pyroelectric detection. The pyroelectric properties of these ceramic materials are pioneer results in this area. (author)
[en] We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, NaxWO3 by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of NaxWO3 reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in NaxWO3
[en] We show evidence of the manifestation of enormous metal-insulator switching ranging up to almost six orders of magnitude in individual nanowires of β'-CuxV2O5. The magnitude and temperature of the phase transition is in strong contrast to data reported over several decades for other Wadsley-type mixed valence tunnel bronze structures.
[en] Structural changes occurring within non-conventional Dawson-type [α/β-Mo18O54(SO3)2]4− polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties. - Graphical abstract: Structural changes occurring within non-conventional Dawson-type [α/β-Mo18O54(SO3)2]4− polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties. Highlights: ► Spectroscopy studies of non-conventional Wells–Dawson polyoxometalates (POMs) at high temperature and high pressure. ► Discussion on the stability of two POM isomers. ► Local formation of bronze-like materials: possibilities for a new synthetic method at high pressure from POM precursors.