1,721,001 research outputs found
Carbon dioxide in pollucite, a feldspathoid with the ideal composition (Cs,Na)16Al16Si32O96•nH2O
No full textWe report a single-crystal Fourier-transform infrared (FTIR) study of a sample of pollucite from Maine, USA. Prior to our work, the sample had been characterized by single-crystal X-ray diffraction, neutron diffraction and electron-probe microanalysis. It is cubic Ia3d, with a crystal-chemical formula Na 1.93(Cs 10.48Rb 0.31K 0.04) Σ=10.83(Al 14.45Si 33.97) Σ=48.42O 96•3.92H 2O, and an H 2O content, determined by thermogravimetric analysis, of 1.6 wt.%. The single-crystal FTIR spectrum has a doublet of intense bands at 3670 and 3589 cm -1, which are assigned to the n 3 and n 1 stretching modes of the H 2O molecule, respectively. A very intense and sharp peak at 1620 cm -1 is assigned to the n 2 bending vibration. In the near-infrared region there is a relatively intense peak at 5270 cm -1, which is assigned to a combination (ν 2 + ν 3) mode of H 2O, and a weak but well defined doublet at 7118 and 6831 cm -1, which is assigned to the first overtones of the fundamental stretching modes. A relatively weak but extremely sharp peak at 2348 cm -1 shows that the pollucite contains CO 2 molecules in structural cavities. Mapping the sample using FTIR indicates that both H 2O and CO 2 are homogeneously distributed. Secondary ion mass spectrometry yielded an average CO 2 content of 0.09±0.02 wt.%. On the basis of this value, we determined the integrated molar absorption coefficient for the spectroscopic analysis of CO 2 in pollucite to be e iCO2 = 11,000±3000 l mol -1 cm -2; the linear molar absorption coefficient for the same integration range is e lCO2 = 1600±500 l mol -1 cm -1
Observation of Charge-Density-Wave Excitations in Manganites.
No full textIn the optical conductivity of four different manganites with commensurate charge order (CO), strong peaks appear in the meV range below the ordering temperature TCO. They are similar to those reported for one-dimensional charge density waves (CDW) and are assigned to pinned phasons. The peaks and their overtones allow one to obtain, for La1-n/8Can/8MnO3 with n=5, 6, the electron-phonon coupling, the effective mass of the CO system, and its contribution to the dielectric constant. These results support a description of the CO in La-Ca manganites in terms of moderately weak coupling and of the CDW theory
High-pressure far-infrared absorption measurements on La(1-x)Ca(x)MnO(3) by means of synchrotron radiation
No full textNorth American microtektites are more oxidized than tektites
No full textIron oxidation states and coordination numbers have been determined by micro-X-ray absorption near edge spectroscopy (XANES) on the cores of a large group of microtektites from the Australasian, Ivory Coast, and North American (NA) tektite strewn field. The North American microtektites used in this study have been collected from five sites at different distances from the source crater; most have SiO2 content between 70 and 80 wt%. Accurate analysis of the pre-edge peak energy position and integrated area allowed determination of Fe3+/(Fe2++Fe3+) ratios on all samples with an estimated error of +/- 0.05.
Microtektites from the Australasian and Ivory Coast strewn fields show low values of the Fe3+/(Fe2++Fe3+) ratios, in fair agreement with tektites from the same strewn field. In contrast, microtektites from the North American strewn fields show a wide range of Fe3+/(Fe2++Fe3+) ratios from 0.02 to ca. 0.61. Comparison of Fe oxidation state data with chemical composition do not show any relation between Fe3+/(Fe2++Fe3+) ratios and Na, Ca, or K contents, thus suggesting that the high-Fe oxidation states are not the consequence of sea-water alteration.
The difference between the Fe oxidation state of tektites and microtektites from the North American strewn fields suggests that some factors in the formation of the North American microtektites were different than for the North American tektites and for microtektites in the other strewn fields.
Previous Fe oxidation state data on NA tektites strongly suggest that the wide range in Fe oxidation state we found on NA microtektites is not related to lateral heterogeneity of the target rocks. Despite a correlation between microtektite oxidation state and distance from the source crater, we maintain that Fe oxidation state is not related only to the microtektite droplet flight distance. This is in keeping with the fact that no significant variations in the Fe oxidation state have been found in microtektites from the Australasian strewn field, even for Australasian microtektites recovered in Antarctica. The Fe oxidation state in North American microtektites could be explained by interaction of melt droplets with a H2O-rich vapor plumes generated during the impact. These data point out that some difference must exist between the thermal histories of microtektites and tektites from the NA strewn field. Moreover, microtektites from the NA strewn field show also distinctively higher oxidation states than those from Ivory Coast or the Australasian strewn fields
Spectral distribution of infrared synchrotron radiation by an insertion device and its edges: A comparison between experimental and simulated spectra
No full textThe first measurements of the spectral distribution of infrared radiation emitted by an undulator are reported. They are compared with calculations including both velocity and acceleration terms. Measurements have been performed at the beam line SIRLOIN (Spectroscopie en InfraRouge Lointain). The agreement between the observations and this first exact numerical solution shows that the inclusion of the velocity term in the submillimeter frequency range is necessary. Moreover, structures due to undulator edges are observed in the far infrared and mid-infrared range, while the interference pattern due to redshifted harmonics of the undulator is dominating in the mid-infrared to near infrared
Staggered magnetization, critical behavior, and weak ferromagnetic properties of LaMnO3 by muon spin rotation
No full textWe present a study of a microtwinned single crystal of LaMnO3 by means of implanted muons. Two muon stopping sites are identified from the symmetry of the internal field in the ordered phase. The temperature dependence of these fields yields the behavior of the staggered magnetization,. from which a static critical exponent [beta =0.36(2)] is extracted and discussed. The muon spin-spin relaxation rate shows a critical slowing down (contrary to preliminary findings), with a critical exponent n = 0.7(1), demonstrating the Ising nature of the dynamic fluctuations. The muon precession frequencies vs the applied magnetic field reveal the saturation of the weak ferromagnetic domain structure originated by the Dzialoshinski-Moriya antisymmetric exchange
PRESS-MAG-O: a unique instrument to probe materials and phenomena under extreme conditions at Frascati
No full textPRESS-MAG-O is a new instrument under commission at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) designed to investigate materials under extreme conditions. The instrument, once completed, will allow combining high harmonic AC magnetic susceptibility measurements and magneto-optic experiments on samples under high pressures (HP), with a variable DC magnetic field in a wide temperature range. The system is designed to work at SINBAD, the IR synchrotron radiation beamline operational since 2001 at DA phi NE (Double Annular phi-factory for Nice Experiments), the storage ring of the Laboratori Nazionali di Frascati of the INFN. HP will be applied up to about 20GPa to samples inside a Cu-Be diamond anvil cell designed to allow concurrent FTIR experiments and high harmonic AC susceptibility measurements in a DC magnetic field up to 8T and in a wide temperature range
Pressure dependence of the phonon spectrum of la1-xCa xMnO3-δ manganites
No full textThe pressure dependence of the phonon spectrum of three La1 - xCaxMnO3 - δ manganites have been studied by means of Far-IR absorption spectroscopy coupled with a Diamond Anvil Cell. The effect of the applied pressure on the charge delocalization have been investigated defining the nature of the metallization process in the low-frequency domain
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