Results 1 - 10 of 19597
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[en] Recent experiments have demonstrated that valence band dispersion may be observed on suitably prepared surfaces of quasicrystals. We present model calculations for optical transitions for one-dimensional a periodic lattices, and show that these calculations are consistent with the experimental photoemission results. We estimate the total number of bands which can be observed in such an experiment is reduced from infinite, to just two to three bands in a typical experiment
[en] The morphological and electrical properties of Ba1-xSrxCe0.8Y0.2O3-δ with x varying from 0 to 1 prepared by a modified Pechini method were investigated as potential high temperature proton conductors. Dense microstructures were achieved for all the samples upon sintering at 1500 C for 5 h. The phase structure analysis indicated that perovskite phase was formed for 0 (le) x (le) 0.2, while for x larger than 0.5, impurity phases of Sr2CeO4 and Y2O3 appeared. The tolerance to H2O for the samples improved with the increase in Sr content when exposed to boiling water, while the electrical conductivity decreased from x = 0 to 1. However, the resistance to CO2 attack at elevated temperatures was not improved within the whole x range studied.
[en] The crystallographic and electronic structure of UFe2Al10 was studied as a function of pressure by combining X-ray diffraction results with the full potential linearized augmented plane wave (LAPW) calculations method. The volume-pressure reduction measured at 23.5 GPa is V/V0 = 0.87, with a B0 value of 132 ± 8 GPa. The uranium 5f electrons in this compound are located in a narrow and well-defined band above EFermi, having a very weak interaction with the iron 3d band located below EFermi. Consequently, the DOS at EFermi is close to zero, indicating a close to zero-magnetic moment of the uranium atom at low temperature up to a pressure of 23.5 GPa, as expected from the layered crystallographic structure of this compound. The above assumption is supported by preliminary neutron diffraction data, where no long-range magnetic order was detected down to 3 K.
[en] A series of crystalline Gd-W oxides, with Gd:W ratios spanning the values 0.1-3.5, has been prepared and treated with a flow of NH3(g) in the temperature range 700-1100 C. Besides the previously reported formation of GdWO3N and Gd2WO3N2, the following new results were obtained: (i) cubic Gd0.1WO3 upon ammonolysis forms an (oxy)nitride Gd0.1W(O, N)x with an f.c.c. lattice; (ii) the previously described Gd2WO3N2 exhibits a solid solubility range Gd3-xW1+x(O, N)y with, approximately, 0≤x≤1; (iii) ammonolysis of Gd14W4O33 yields an oxynitride, the composition of which varies with the synthesis temperature according to Gd14W4O33-xNy(0≤x≤17±2, 0≤y≤9±2). All strong diffraction lines, including those of the pure oxide (x=y=0), can be indexed with a body-centred monoclinic unit cell derived from that of fluorite. For Gd14W4O33 the cell parameters are a=5.3592(11), b=3.7295(7), c=3.8636(8) A, β=92.170(2) and V=77.17 A3. However, strong superstructure reflections in the electron diffraction patterns indicate that the true unit cell is considerably larger. A partial structure determination of Gd14W4O33-xNy has been carried out by the Rietveld method. Magnetic susceptibility measurements in the temperature interval 15-300 K show a Curie-Weiss law behaviour for Gd14W4O33-xNy, with μeff=8.08±0.06 Bohr magnetons per Gd3+ and θ=-12.4±1.1 K for all compositions. (orig.)
[en] The Ru-Sn liquid-solid and some solid-solid equilibria have been completely revised by means of differential thermal analysis, X-ray powder diffraction and microprobe investigations. The existence of two intermetallic phases has been clearly established: Ru0.4Sn0.6 decomposed by a peritectic reaction at 1266(±4) C and Ru0.3Sn0.7 congruently melting at 1257(±2) C. (orig.)
[en] The standard enthalpies of formation of LuSi, Lu5Sn3 and Lu5Ge3 have been remeasured by direct synthesis calorimetry at 1473 ± 2 K. The following ΔHof (kJ mol-1) values of atoms are reported: LuSi -79.1±2.7; Lu5Sn3 -75.1±2.7; Lu5Ge3 -93.1±2.2. The results are compared with our previously reported values. (orig.)
[en] The magnetic properties of alkali metal uranates(V) MUO3 (M, alkali metal) with the perovskite structure have been studied. In this study RbUO3 (cubic perovskite structure) was prepared and its magnetic susceptibility was measured from 4.2 K to room temperature. It was found that a magnetic anomaly (magnetic transition) occurred at about 27 K. As a result of the U5+ ion in the paramagnetic state, the electron paramagnetic resonance spectrum was not observed even at 4.2 K. The magnetic susceptibility results and the optical absorption spectrum were analysed on the basis of an octahedral crystal field model. The magnetic transition temperatures and crystal field parameters determined for MUO3 (M triple bond Li, Na, K, Rb) are compared and discussed. (orig.)
[en] The La-Ru system has been examined to search for new superconducting phases in addition to the previously known superconductor LaRu2. Electrical resistivity measurements reveal that La3Ru (Fe3C structure type), La5Ru2 (Mn5C2 structure type) and La7Ru3 (Sr7Pt3 structure type) exhibit superconductive transitions at 5.55, 3.35 and 1.75 K, respectively. Magnetic susceptibility measurements give estimates of the lower and upper critical field at selected temperatures for the three phases. Pauli-like paramagnetism in the normal state for all compounds is observed. (orig.)
[en] Recently, the synthesis of a novel ferromagnetic compound with a high Curie temperature of 655 C and the approximate stoichiometry GdFe8.4Ge1.6, has been reported in this Journal. The work reported here shows that samples prepared with identical experimental conditions are not actually single-phase, but three-phase mixtures containing a majority substitutional solid solution of germanium in α iron (85.3% wt.), GdFe2Ge2 (12.3% wt.), and a small proportion of the hexagonal polymorph of Fe3Ge (2.4% wt.), as shown by X-ray diffraction, scanning electron microscopy and thermomagnetic measurements. (orig.)