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1.
Optical absorption and electrical resistivity of amorphous Ge20Se60Sb20 films are investigated as a function of the thermal annealing. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation (h) = B(h–Eo)2. Increasing the annealing temperature from 423 K to 553 K, decreases the optical gap of the film from 1.25 eV to 0.78 eV. The effect of annealing temperature on high frequency dielectric constant () and carrier concentration (N) was also studied. As a result of annealing the film at 533 K, the electrical resistivity and activation energy for conduction decreased from 5.7 × 107 to 2.9 × 102 ·cm and from 0.94 to 0.34 eV, respectively. The crystalline structures resulting from heat treatment at different elevated temperatures have been studied by X-ray Diffraction (XRD). The optical and electrical changes were attributed to the amorphous-crystalline transformations in the chalcogenide films.  相似文献   

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The ordinary X-ray diffraction profile and anomalous X-ray scattering profiles at nickel and germanium K absorption edges of amorphous Al60Ge30Ni10 alloy have been determined. The results indicate the characteristic feature of the coexistence of nickel-rich highly ordered crystal-like regions and germanium-rich amorphous regions. From the environmental radial distribution function around germanium atoms, the coordination number around a germanium atom is estimated at about 4. Thus, an amorphous germanium-like structure may be quite feasible in this region.  相似文献   

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机械合金化制备Nd60 Fe20 Al10 Co10非晶粉末的研究   总被引:1,自引:0,他引:1  
鲁小川  徐晖  阳松平  董远达 《功能材料》2003,34(6):647-648,651
利用机械合金化制备Nd60Fe20Al10Co10非晶粉末,采用X射线衍射(XRD)和振动样品磁强计(VSM)研究Nd60Fe20Al10Co10非晶的形成过程、磁性能变化及其与成分结构的关系。结果表明,90min后Al原子溶入Nd原子形成固溶体。球磨2h后出现少量非晶,20h后Co单质和Nd单质消失.组织为非晶相(含少量的α-Fe)。球磨100h最终得到非晶 少量的α-Fe纳米晶。球磨过程中,矫顽力随着合金中非晶的量增加而升高.球磨20h矫顽力达到43kA/m。Nd60Fe20Al10Co10合金具有硬磁性是由于非晶相的存在而造成的。  相似文献   

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Crystallization of amorphous Te-20 at. % Pb alloy obtained by rapid cooling from the liquid state was investigated by differential thermal analysis, X-ray diffraction and transmission electron microscopy. It was found that crystallization, beginning at 337 K, is of a continuous nature and proceeds over a fairly wide temperature range. At the first crystallization stage, nucleation of the metastable phase MS I, with hexagonal structure and lattice parametersa = 4.49 Å andc = 5.85 Å, takes place. Contrasts observed in the micrographs of single crystals of phase MS I were interpreted as areas with increased concentration of Pb atoms. With rising temperature, the phase present in these areas dissolves, and in its place platelet precipitates of the compound PbTe appear. In this paper, a sequence of decomposition for the amorphous phase obtained in the Te-20 at. % Pb alloy, as well as a model for the precipitation of PbTe, are proposed.  相似文献   

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Doping with low concentrations (∼0.01 at % and below) of Gd and Pb is shown to have little effect on the lattice thermal conductivity χph of extruded Bi85Sb15. This finding suggests that the χph of solid solutions can be determined using doping with low concentrations of electroactive impurities. Original Russian Text ? Z.F. Agaev, G.D. Abdinova, G.Z. Bagieva, M.M. Tagiev, D.Sh. Abdinov, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 137–139.  相似文献   

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Bulk Zr60Cu20Pd10Al10 amorphous alloy was rolled at room temperature up to 96% reduction in thickness without fracture. The changes of microstructure and hardness during rolling deformation were investigated by X-ray diffraction, differential scanning calorimetry, high-resolution transmission electron microscopy, and microhardness measurement. It is revealed that the rolling deformation causes the quenched-in nuclei in the glass to grow slowly before a deformation degree of 90%. Substantial nanocrystallization occurs at higher deformation degree, where the softening induced by shear bands can even be compensated by the nanocrystallization.  相似文献   

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杨承波  张兴国  张伟  季首华 《功能材料》2006,37(8):1352-1354
采用X射线衍射(XRD)、示差扫描量热分析(DSC)、显微硬度测量、四点探针测量电阻法和动态极化曲线法,研究了Ni60Nb(20-x)TaxTi15Zr5 系列非晶合金的结构、热稳定性、力学性能、导电性和耐腐蚀性能.研究表明随着Ta含量的增加,合金的热稳定性、力学性能、耐腐蚀性能变好,对导电性影响不大.当Ta完全代替Nb时性能最优,具有宽过冷液相区(67K),很高的显微硬度(1100HV)和电阻率(220μΩ·cm),很低的钝化电流密度(0.01A/m2).  相似文献   

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A nearly pure 2223 phase of the ceramic superconductor Bi1.8Pb0.3Sb0.1Sr2Ca2Cu3O10?δ was obtained by solid-state reaction in air. The samples showed a semiconducting behavior when the temperature was higher than 140 K. The electrical resistance began to drop at 140 K and went to zero at 92 K. Their a.c. magnetic susceptibility showed two transitions at 130 and 89 K, but the 110 K transition was absent. These transitions were stable during cycling for three times from 77 K to room temperature. X-ray diffraction revealed that there was no 2212 or 2201 phase in these samples but only a small amount of monoclinic phase before and after cycling from 77 K to room temperature. SEM images showed that the grains of the monoclinic phase segregated on the surface of the sample and at the grain boundaries inside the sample, which is the reason for the sample's poor superconductivity and the decrease in zero resistance. Evidence from TEM and SEM equipped with a wavelength dispersive meter indicated distortion of the 2223 phase. These distorted 2223 crystals may be responsible for the 130 K superconductivity.  相似文献   

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《Vacuum》2012,86(4):480-482
In the present communication, d.c. conductivity of a-Se80Te20 and a-Se80Te10M10 (M = Cd, In, Sb) alloys has been studied in the temperature range 225–311 K in order to identify the conduction mechanism and to analyze the effect of different metallic additives on d.c. conduction in a-Se80Te20 alloy below the room temperature. An analysis of the experimental data confirms that conduction in low temperature region is due to variable range hopping in localized states near the Fermi level. The Mott parameters have been calculated in a-Se80Te20 and a-Se80Te10M10 (M = Cd, In, Sb) alloys. The experimental data is found to fit well with Mott condition of variable range hopping conduction.  相似文献   

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Amorphous thin films of the ternary compound In33Se33Sb33 have been produced by a vacuum evaporation technique. The optical gap Egopt of In33Se33Sb33 thin films is measured as a function of temperature of heat treatment. It was found that the optical gap has a higher value than that of the binary compound In50Se50 at the initial stages of heat treatment, but after a particular temperature (423 K) of heat treatment, the value of optical gap decreases appreciably in the case of In33Se33Sb33 thin films, while it increased in the case of In50Se50 thin films.  相似文献   

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A nearly pure 2223 phase of the ceramic superconductor Bi1.8Pb0.3Sb0.1Sr2Ca2Cu3O10– was obtained by solid-state reaction in air. The samples showed a semiconducting behavior when the temperature was higher than 140 K. The electrical resistance began to drop at 140 K and went to zero at 92 K. Their a.c. magnetic susceptibility showed two transitions at 130 and 89 K, but the 110 K transition was absent. These transitions were stable during cycling for three times from 77 K to room temperature. X-ray diffraction revealed that there was no 2212 or 2201 phase in these samples but only a small amount of monoclinic phase before and after cycling from 77 K to room temperature. SEM images showed that the grains of the monoclinic phase segregated on the surface of the sample and at the grain boundaries inside the sample, which is the reason for the sample's poor superconductivity and the decrease in zero resistance. Evidence from TEM and SEM equipped with a wavelength dispersive meter indicated distortion of the 2223 phase. These distorted 2223 crystals may be responsible for the 130 K superconductivity.  相似文献   

16.
Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500~mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity Hc of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.  相似文献   

17.
A new tetragonal long period anti-phase boundary structure is described in Pt3V. It consists of a regular alternation of DO22 and Ll2 unit cells in the proportion 1:1. It suggests that, depending on the temperature of annealing, a sequence of structures occurs in Pt3V, each consisting of DO22 and Ll2 structural elements in varying proportion, the two end members being DO22 at low temperature and Ll2 at high temperature.  相似文献   

18.
Catalytic activities of La0.7Pb0.3MnO3 and La0.7Sr0.3MnO3 for the oxidation of CO were determined for unsupported samples and for samples supported on corrugated monoliths of cordierite. Pt free La0.7Sr0.3MnO3 was produced with a high surface area. It is stable to ≥ 1000°C and has been used to prepare supported devices having overall activities comparable to commercial Pt catalysts. In contrast, the “intrinsic” activity of La0.7Pb0.3MnO3 is in most samples markedly reduced at ≥ 400°C. The effects of Pt on the activity for CO oxidation were studied. Single crystals of La0.7Pb0.3MnO3 having 0–5200 ppm of Pt were grown. Polycrystalline samples having 0–2200 ppm of Pt were prepared, mainly by freeze-drying techniques. Samples with ≤ 570 ppm Pt were not significantly more active than the “intrinsic” freshly prepared perovskite surfaces without Pt showing that the activity of the perovskite is not directly connected with Pt. Samples with ≥ 1600 ppm Pt showed markedly enhanced activity and a higher activation energy similar to that of Pt.  相似文献   

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Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20, 55%, was observed in the MTJs after annealing at 270℃for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity HC of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.  相似文献   

20.
Mg-based amorphous alloys are one of the potential hydrogen storage materials but suffer from sluggish dehydrogenation/hydrogenation(de/hydrogenation)kinetics.In this work,as a new strategy,a hydrogen pump is built on the surface of amorphous alloys to solve this problem.By milling crystalline YFe2-xAlx hydrogen storage alloy with Mg60La10Ni20Cu10 amorphous alloy,fine crystalline particles were seeded on amorphous alloy powder to form a\"strawberry\"structure.According to the TEM observation,a metal-lurgical bonding boundary formed between the Mg-based amorphous matrix and the Y-Fe-Al crystalline alloy.By microstructure and de/hydrogenation kinetics investigation,the\"hydrogen pump\"effect of the seeded crystalline alloy was confirmed,which makes it much easier for the hydrogen to dissociate on and diffuse through the surface of the Mg-based amorphous alloy.With such effect,the H absorption rate of Mg60La10Ni20Cu10 amorphous alloy became almost eight times faster and it absorbs~2.8 wt.%in 1 h at 130 ℃ under 4.5 MPa-H2.Further,fast hydrogenation can even achieve at 70 ℃ and the low-temperature dehydrogenation kinetics of the amorphous hydride can be also greatly promoted.The present work proves that surface modification is of great importance for obtaining Mg-based amorphous alloy with ideal hydrogen storage performance.  相似文献   

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