Search results for "SSBA"
showing 10 items of 454 documents
The interaction of S,N-coordinated dimethyltin(IV) derivatives with deoxyribonucleic acid: Structure and dynamics by119Sn mössbauer spectroscopy
1999
Complexes Me2SnCl(SPy) and Me2SnCl(SPym) (HSPy = 2-mercaptopyridine; HSPym = 2-mercaptopyrimidine), from ethanol solutions, interact with aqueous calf-thymus DNA yielding condensed phases with probable Me2Sn(SPy,-SPym) (DNA monomer) stoichiometries of 1:1; the condensation of DNA is inferred originated from electrostatic bonding between complex cations Me2Sn(SPy,SPym)+ and the phosphate oxygen of the phosphodiester groups. Octahedral-or trigonal-bipyramidal tin environments are inferred from the point-charge model treatment of the 119Sn Mössbauer parameter nuclear quadrupole splitting, considering the bonding by S and N, or only S donor atoms from the ligand, as well as possible coordinatio…
In situ Mössbauer spectroscopy: Evidence for green rust (fougerite) in a gleysol and its mineralogical transformations with time and depth
2005
Abstract A miniaturized Mossbauer spectrometer, adapted to the Earth’s conditions from the instrument developed for Mars space missions, has been used for the first time to study in situ variations with depth and transformations with time of iron minerals in a gleysol. The instrument is set into a PVC tube and can be moved up and down precisely (±1 mm) at the desired depth. Mossbauer spectra were obtained from 15 to 106 cm depth and repeated exactly at the same point at different times to follow mineralogical transformations with time. X-ray diffraction (XRD) and selective extraction techniques were performed on soil samples. The piezometric level of the water table was measured and the com…
Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions
2018
Iron oxides are among the major constituents of the deep Earth’s interior. Among them, the epsilon phase of Fe2O3 is one of the less studied polymorphs and there is a lack of information about its structural, electronic and magnetic transformations at extreme conditions. Here we report the precise determination of its equation of state and a deep analysis of the evolution of the polyhedral units under compression, thanks to the agreement between our experiments and ab-initio simulations. Our results indicate that this material, with remarkable magnetic properties, is stable at pressures up to 27 GPa. Above 27 GPa, a volume collapse has been observed and ascribed to a change of the local env…
All-fiber noninterferometric narrow-transmission-bandpass filter
2012
In-fiber mode engineering based on the combination of Bragg and long-period gratings (LPGs) permits the implementation of noninterferometric transmission filters with narrow passbands using standard single-mode fiber. The design of the bandpass filter is based on the coupling between propagating and counterpropagating cladding modes in two fiber Bragg gratings. A LPG located between the Bragg gratings transfers power from the input fundamental mode to a specific cladding mode and recouples the filtered signal to the output fundamental mode. The filter produces a series of narrow passbands of about 30 pm linewidth with a maximum transmittance above 60%, 20 dB isolation, and passband separati…
Polarized neutron diffraction and Mössbauer spectral study of short-range magnetic correlations in the ferrimagnetic layered compounds(PPh4)[FeIIFeII…
2002
Short-range antiferromagnetic correlations have been studied in the layered compounds (PPh 4 ) [Fe I I Fe I I I (ox) 3 ] and (NBu 4 ) [Fe I I Fe I I I (ox) 3 ] by neutron polarization analysis and Mossbauer spectroscopy. Polarized neutron diffraction profiles obtained between 2 and 50 K on (d 2 0 -PPh 4 ) [Fe I I Fe I I I (ox) 3 ] show no magnetic Bragg scattering; the lack of such scattering indicates the absence of long-range magnetic order. However, a broad asymmetric feature observed at a Q of ca. 0.8 A - 1 is attributed to two-dimensional short-range magnetic correlations, which are described by a Warren function. The correlation length is ca. 50 A between 2 and 30 K and then decreases…
Effect of cation disorder on the magnetic properties ofSr2Fe1−xGaxReO6(0<x<0.7)double perovskites
2007
The effect of diamagnetic dilution of the Fe sublattice on the structural and magnetic properties of the double perovskite Sr{sub 2}Fe{sub 1-x}Ga{sub x}ReO{sub 6} (0 =}0.4 is detected by x-ray structural analysis accompanied by the observation of a magnetically ordered and a paramagnetic phase in the corresponding Moessbauer spectra. Below 20% Ga content, Ga statistically dilutes the -Fe-O-Re-O-Fe- double-exchange pathways. Phase separation begins at 20% Ga substitution; between 20% and 40% ofmore » Ga content, the paramagnetic Ga-based phase does not contain any Fe. The Fe-containing, paramagnetic cubic phases which can be detected by Moessbauer spectroscopy first appear for x=0.4.« less
Mössbauer Spectral Study of Two Layered Honeycomb Molecular Magnets: PPh4FeIIFeIII(ox)3 and NBu4FeIIFeIII(ox)3
2002
The Mossbauer spectra of the layer ferrimagnets PPh4FeIIFeIII(ox)3 and NBu4FeIIFeIII(ox)3 have been measured between 1.9 and 315 K. The paramagnetic spectra exhibit both high-spin iron(II) and iron(III) doublets. The iron(II) quadrupole splittings are negative and decrease substantially upon cooling as a result of a low-symmetry crystal field splitting. In contrast, the iron(III) splittings are small, positive, and virtually independent of temperature. The respective magnetic ordering temperatures of 30 and 42.5 K agree well with the phase observed by bulk magnetometry and the magnetic sextets yield hyperfine fields of ca. 60 kOe for iron(II) and 540 kOe for iron(III). The unusually low iro…
Zerstörungsfreie Phasenanalyse dünner Oberflächenschichten mittels Konversionselektronen
1987
By use of an appropriate gamma radiation, conversion electrons may be produced by Mossbauer effect also in a depth below the sample surface deeper than the free path for inelastic electron scattering. Because the Mossbauer spectrum of the conversion electrons reflects the local phase composition, the recording of all electrons escaping from the surface allows an integral phase analysis of a layer of some 10–100 nm thickness. If only electrons within a narrow range of energy are recorded, a depth selective phase analysis is possible. The applicability of these two techniques of conversion electron spectroscopy is demonstrated by a few examples concerning oxidation and passivation of steel. C…
Mössbauer study of properties and phase transitions of Cd2Nb2–2xSn2xO7–2xF2x
1973
With the aid of Mossbauer spectroscopy the solid solution series Cd2Nb2–2xSn2xO7–2xF2x are investigated in the temperature range 4.2 to 400 K. The crystal structure belongs to the cubic pyrochlore type. The BY6 octahedra (B = Nb, Sn; Y = O, F) are linked three-dimensionally through their corners, forming groups of four octahedra which are extended or compressed in the (111)-direction for x ≤ 0.375 or x ≥ 0.400 respectively. The dependence of the quadrupole splitting ΔEQ on x shows a small but significant discontinuity in the region 0.375 < x < 0.400. This can be attributed to a first order phase-transition which depends on concentration, but not on temperature over the temperature region st…
Spin crossover star-shaped metallomesogens of iron(II).
2014
Three new types of spin crossover (SCO) metallomesogens of Fe-II based on symmetric tripod ligands and their magnetic and structural properties are reported here. These were obtained by condensation of tris(2-aminoethyl)-amin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine (mpyN, N (number of carbon atoms in n-alkyl chains) = 8, 18), 1-alkyl-1H-imidazole (imN, N = 4, 16, 18, 20, 22), or 1-alkyl-1H-benzimidazole (bimN, N = 6, 14, 16, 18, 20). A complex derived from 1-octadecyl-1H-naphtho[2,3-d]imidazole (nim18) retains the high spin state at any temperature. Single crystals of the short-chain complexes were investigated by a combination of X-ray crystallography, magnetic meas…