169 resultados para Ce^3
Resumo:
A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Nitrogenation leads to a relative volume expansion of about 6%. The lattice constants and unit cell volume decrease with increasing rare-earth atomic number from Nd to Dy, reflecting the lanthanide contraction. On average, the Curie temperature increases due to the nitrogenation to about 200 K compared with its parent compound. Generally speaking, nitrogenation also results in a remarkable improvement of the saturation magnetization and anisotropy fields at 4.2 K and room temperature for R3Fe29-xVxN4 compared with their parent compounds. The transition temperature indicates the spin reorientations of R3Fe29-xVxN4 for R = Nd and Sm are at around 375 and 370 K which are higher than that of R3Fe29-xVx, for R = Nd and Sm 145 and 140 K, respectively. The magnetohistory effects of R3Fe29-xVxN4 (R = Ce, Nd, and Sm) are observed in low fields of 0.04 T. After nitrogenation the easy magnetization direction of Sm3Fe26.7V2.3 is changed from an easy-cone structure to the b-axis. As a preliminary result, a maximum remanence B-r of 0.94 T, an intrinsic coercivity mu(0)H(C) of 0.75 T, and a maximum energy product (B H)(max) of 108.5 kJ m(-3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.
Resumo:
Ce-Ce-MCeO_2Ce_(1-x)M_xOMCeO_2xCaLaNiMnCe-Ni_(0.7)Ce_(0.3)OZrO_2CH_41Ce-Ca-La-OCaLaCeO_2CeO_2100H_2-TPRCaLaCeO_2Ce-La-Ca-OLaCe-Ca-OCe-La-OHZTPRCe-Ca-O2Ce-Ni-Mn-ONiOMnO_xCeO_2lCeO_2-MnO_xCe_(0.8)Mn_(0.2)ONiONi-1050550CH_4CO_22CeO_2-NiOCe_(0.3)Ni_(0.7)O530CH_4CO_2Mn550oCCH4C023NIOMnoxNioIMn090CeNioICeyMno9003y08530oCy053Ni-Ce-OZrOZ1Ni1-xCexOCeOZNIO2CeOZNIOcH4CeCe30Nio7Ceo3O530oC3Ni07Ceo3O900oC540oCCH4COZ4PdNi07Ceo30PdA12O35Ni07Ce03OZrOZ5102ZrOZ5102NIOCeOZMgOA1203NIOCeOZ6Nio7Ceo3OZrOZNio7Ceo3O50Ni4ZroCeZO37Nio7Ceo3O50ZrOZZrOZZr02Ce4PrCeO2YSZ
Resumo:
Alternating layers of Si(200 angstrom thick) and Ce(200 angstrom thick) up to 26 layers altogether were deposited by electron evaporation under ultrahigh vacuum conditions on Si(100) substrate held at 150-degrees-C. Isothermal, rapid thermal annealing has been used to react these Ce-Si multilayer films. A variety of analytical techniques has been used to study these multilayer films after annealing, and among these are Auger electron spectroscopy, Rutherford backscattering, X-ray diffraction, and high resolution transmission electron microscopy. Intermixing of these thin Ce-Si multilayer films has occurred at temperatures as low as 150-degrees-C for 2 h, when annealed. Increasing the annealing temperature from 150 to 400-degrees-C for 1 h, CeSi2 forms gradually and the completion of reaction occurs at approximately 300-400-degrees-C. During the formation of CeSi2 from 150-400-degrees-C, there is some evidence for small grains in the selected area diffraction patterns, indicating that CeSi2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial CeSi2 layers, only polycrystals were formed when reacted in the solid phase even after rapid thermal anneal at 900-degrees-C for 10 s. The formation mechanism has also been discussed in combining the results of the La-Si system.
Resumo:
Planar punch through heterojunction phototransistors with a novel emitter control electrode and ion- implanted isolation (CE-PTHPT) are investigated. The phototransistors have a working voltage of 3-10V and high sensitivity at low input power. The base of the transistor is completely depleted under operating condition. Base current is zero. The CE-PTHPT has an increased speed and a decreased noise. The novel CE-PTHPT has been fabricated in this paper. The optical gain of GaAlAs/GaAs CE-PTHPT for the incident light power 1.3 and 43nw with the wavelength of 0.8 mu m reached 1260 and 8108. The input noise current calculated is 5.46 x 10(-16) A/H-z(1/2). For polysilicon emitter CE-PTHPT, the optical gain is 3083 at the input power of 0.174 mu w. The optical gain of InGaAs/InP CE-PTHPT reaches 350 for an incident power of 0.3 mu w at the wavelength of 1.55 mu m. The CE-PTHPT detectors is promising as photo detectors for optical fiber communication system.
Resumo:
Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.
Resumo:
The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.
Resumo:
42 0MeV82 Se1 39La1 4 2 Ce . 2 62 5,2 995 3 83 4keV 3 , 8+,9(- ) 1 1 (- ) .N=84 .1 4 2 Ce , . ,1 4 2 Ce
Resumo:
10 2MeV16O6+117Sn , 4n12 9Ce. .Ce ,16O117Sn118Sn116Sn , 3Ce . 4.1min12 9Ce.X - -t - -t , 5 112 9Ce (EC/ +) . ,12 9Ce12 9La ( 2 6 7) %12 9La 2 78.6keV .La K X6 8.2keV
Experimental study of the U-238(S-36,3-5n)(269-271)Hs reaction leading to the observation of (270)Hs
Resumo:
The deformed doubly magic nucleus (270)Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg-26+Cm-248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of (270)Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca-48+Ra-226 and S-36+U-238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction S-36+U-238 that are similar to those of the Mg-26+Cm-248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S-36+U-238 and the observation of (270)Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8(-0.7)(+2.6) pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg-26+Cm-248 reaction at similar excitation energy.
Resumo:
(Y0.95Ln(0.01)Ce(0.04))(3)Al5O12 phosphors were synthesized by high-temperature solid state reaction under reducing atmosphere and the doping effects of lanthanide ions (Ln(3+)) on the luminescence properties of phosphors were studied. YAG: Ce, Ln spectra of excitation and emission show that the influence between Ce3+ and Ln(3+) can be divided into the following three types
Resumo:
Mg-5Al-0.3Mn-xCe (x = 0-3, wt.%) alloys were prepared by metal mould casting method. The microstructures and mechanical properties were investigated. The results revealed that the main phases of as-cast Mg-5Al-0.3Mn alloy consist of alpha-Mg matrix and beta-Mg17Al12 phase. With the addition of Ce element, Al11Ce3 precipitates were formed and mainly aggregated along the grain boundaries. The amount of the Al11Ce3 precipitates increased with increasing addition of Ce, but the amount of beta-Mg17Al12 phase decreased. The highest tensile strength was obtained in Mg-5Al-0.3Mn-1.5Ce alloy. The ultimate tensile strength (UTS), yield strength (YS) and elongation at room temperature are 203 MPa, 88 MPa and 20%, separately.
