Optical constants and electrical conductivity of Ge20Se60Sb20 thin films

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–E_o)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.     

X-ray diffraction study of an amorphous Al60Ge30Ni10 alloy

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.     

机械合金化制备Nd60 Fe20 Al10 Co10非晶粉末的研究

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。     

Crystallization of amorphous Te-20 at.% Pb alloy obtained by rapid cooling from the liquid state

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.     

Thermal conductivity of extruded Bi85Sb15 doped with Gd and Pb

Doping with low concentrations (∼0.01 at % and below) of Gd and Pb is shown to have little effect on the lattice thermal conductivity χ_ph of extruded Bi₈₅Sb₁₅. This finding suggests that the χ_ph 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.     

Structure evolution of bulk Zr60Cu20Pd10Al10 amorphous alloy during rolling deformation

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.     

Ni60Nb(20-x)TaxTi15Zr5系列非晶合金性能研究

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).     

The 130 K High-T c superconductor in the system Bi-Sr-Ca-Cu-O doped with Sb and Pb

A nearly pure 2223 phase of the ceramic superconductor Bi_1.8Pb_0.3Sb_0.1Sr₂Ca2Cu₃O_10?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.     

Estimation of Mott parameters in amorphous Se80Te20 and Se80Te10M10 (Cd,In, Sb) alloys

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.     

The variation in optical gap of amorphous In33Se33Sb33 thin films with temperatures of heat treatment

Amorphous thin films of the ternary compound In₃₃Se₃₃Sb₃₃ have been produced by a vacuum evaporation technique. The optical gap Eg^opt 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.     

TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers

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.     

The 130 K High-Tc superconductor in the system Bi-Sr-Ca-Cu-O doped with Sb and Pb

A nearly pure 2223 phase of the ceramic superconductor Bi_1.8Pb_0.3Sb_0.1Sr₂Ca2Cu₃O_10– 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.     

New long period superstructure in Pt3V with M = 32

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.     

86% TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers

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.     

B或N掺杂端部封闭碳纳米管吸附Pt的第一性原理计算

由于碳纳米管（CNTs）载Pt催化剂中,CNTs与Pt纳米颗粒间的交互作用弱,导致两者间导电性较差,并且容易引起Pt脱落或团聚。本文采用第一性原理对Pt原子在CNTs封闭端部的吸附行为进行了研究,发现B掺杂可以使（5,5）型和（9,0）型CNTs与Pt间的平均吸附能分别提高12.7%和19.6%,N掺杂可以使（5,5）型和（9,0）型CNTs与Pt间的平均吸附能分别提高22.4%和18.4%,并且CNTs与Pt间的电荷转移量较管壁吸附也得到了明显提升,同时B或N掺杂使CNTs-Pt体系的稳定性最高可分别提升133.8%和237.3%,说明在CNTs端部掺杂B或N可提高CNTs载Pt催化剂的性能。     

Structural study of amorphous Pd41Ni41Si18 alloy associated with structural relaxation by anomalous X-ray scattering

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.