Formability and Thermal Stability of Ce62Al15Fe8Co15 Bulk Metallic Glass

The formability and thermal stability of Ce62Al15Fe8Co15 bulk metallic glass （BMG） are studied by x-ray diffraction （XRD） and differential scanning calorimetry. The critical diameter of Ce62Al15Fe8Co15 BMG predicted by the parameter γ is about 3.1 mm, which is roughly in agreement with the XRD results. Stability of the BMG is investigated by means of continuous crystallization diagrams obtained from the extension of the Kissinger and Vogel-Fulcher-Tammann （VFT） equations comparatively. It is found that the dependence of crystallization temperature of the BMG on heating rates follows a nonlinear relationship rather than Kissinger and Lasoka＇s linear fittings. The thermal stability of the BMG is investigated by the VFT equation.     

Observation of β-Relaxation in Sub-Tg Isothermally Annealed Al-Based Metallic Glasses

Al85Ni5 Y8Ca2 and Al88Ni5 Y6Co2Fe2 metallic glasses are fabricated by melt spinning. A kink or a small exothermic peak is observed for both the samples isothermally annealed at sub-glass transition temperatures. Temperature modulated differential scanning calorimetry （TMDSC） data disapprove amorphous phase separation. The activation energies derived from Kissinger plots of the exothermic process on DSC curve around glass transition temperature are consistent with those of β-relaxation of metallic glasses.     

Au doped Sb3Te phase-change material for C-RAM device

Au doped Sb₃Te phase-change films have been investigated by means of in situ temperature-dependent resistance measurement. Crystallization temperature of 2 at.% Au doped Sb₃Te has been enhanced to 161 °C, which leads to a better data retention. The physical stability of the film has been improved evidently after adding Au as well. Resistance contrast has been improved to 1.1 × 10⁴, one order of magnitude higher than that of pure Sb₃Te. X-ray diffraction patterns indicate the polycrystalline Au-SbTe series have hexagonal structure, similar with pure Sb₃Te alloy, when Au doping dose is less than 9 at.%.     

Effect of Yttrium Addition on Glass Forming Ability of ZrCuAlSi Alloy

The effect of yttrium addition on glass formation of a ZrCuAlSi alloy is investigated. The maximum diameter 8mm of the glassy rods for （Zr46.3Cu43.3Al8.9Si1.5）100-xYx alloy with x = 2.5 is obtained by copper mould casting. Apparent enhancement of the glass formation ability is found with addition of yttrium, mainly due to the purification of the alloy melt and the suppression of formation of the primary phases by yttrium.     

Crystallization kinetics in new Sb14As29Se52Te5 amorphous glass

Differential scanning calorimetry (DSC) under non-isothermal conditions is used to study the crystallization kinetics of Sb₁₄As₂₉Se₅₂Te₅ chalcogenide glass. In addition, two approaches are used to analyze the dependence of glass transition temperature (T_g) on the heating rate (α). One is empirical linear relationship between (T_g) and ln(α). The second approach is the use of straight line vs. 1/T_g for the evaluation of the activation energy for glass transition. The phases at which the alloy crystallizes after the thermal treatment have been identified by using X-ray diffraction. The diffractogram of the transformed material shows the presence of some crystallites of As, Te, AsSb, As₂Se₃, Sb₂Se₃ and AsSe_.5Te_.5 in the residual amorphous matrix.     

Compression Behaviour of Bulk Metallic Glasses and Binary Amorphous Alloy

The compression properties of Zr41Ti14Cu12.aNi10Be22.5, Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glasses and Ni77P23 binary amorphous alloy are investigated at room temperature up to 24 GPa, 39 GPa and 30.5 GPa, respectively, using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The pressure-volume relationship of Ni77P23 amorphous alloy is consistent well with the second order BirchMurnaghan （B-M） equation within the experimental pressure range. However, under higher pressure, the experimental data of Zr-based specimens deviate from the B-M equation. Compare to the binary amorphous alloy less excess free volume existing in the bulk metallic glass and multi-component atomic configuration results in a two-stage relationship between compressibility and pressure.     

High-Pressure Annealing Effect on Glass Transformation Temperature of Zr41Ti14Cu12.5Ni10Be22.5 Bulk Metallic Glass

Zr41 Ti14 Cu12.5Ni10Be22.5 bulk metallic glasses （BMG） are annealed at a temperature of 603 K under ambient and high pressures in the range of 3-6 GPa. The effect of high pressure annealing on the nanocrystallization process of compressed specimens is investigated by x-ray diffraction, differential scanning calorimetry and transmission electron microscopy. Experimental results show that the grain size of the crystalline phase decreases with the increasing pressure. For the Zr41Ti14Cu12.5Nil0Be22.5 BMG annealing at 603K in the pressure range of 0- 6 GPa, the activation energy 159.68 kJ/mol and the activation volume △V＊ =0.94 cm^3/mol are determined. The mechanism for the effects of the high pressure on the nanocrystallization process of the BMG is discussed.     

Gaseous Hydrogenation and Its Effect on Thermal Stability of Mg63Ni22Pr15 Metallic Glass

Mg63Ni22Pr15 metallic glasses are produced by a single roller melt-spinning technique. The hydrogen absorption and desorption capacities are respectively 0.38 and 0.14 wt% at 313 K obtained by pressure-composition isotherm. The amorphous structure is found to be retained after gaseous hydrogenation. The glass transition temperature, the onset crystallization temperature, and the crystallization temperature of the hydrogenated Mg63Ni22Pr15 metallic glass are 550, 570 and 577K, respectively, much higher than the corresponding values of 440, 470 and 499K of the as-quenched sample. This means that dramatic enhancement of thermal stability occurs in Mg63Ni22Pr15 metallic glass due to hydrogenation.     

Electrical switching and thermal studies on Ge22Te78−xIx chalcohalide glasses: The effect of iodine on network-topology

Investigations on the electrical switching behavior and thermal studies using Alternating Differential Scanning Calorimetry have been undertaken on bulk, melt-quenched Ge₂₂Te_78−xI_x (3≤x≤10) chalcohalide glasses. All the glasses studied have been found to exhibit memory-type electrical switching. The threshold voltages of Ge₂₂Te_78−xI_x glasses have been found to increase with the addition of iodine and the composition dependence of threshold voltages of Ge₂₂Te_78−xI_x glasses exhibits a cusp at 5 at.% of iodine. Also, the variation with composition of the glass transition temperature (T_g) of Ge₂₂Te_78−xI_x glasses, exhibits a broad hump around this composition. Based on the present results, the composition x=5 has been identified as the inverse rigidity percolation threshold at which Ge₂₂Te_78−xI_x glassy system exhibits a change from a stressed rigid amorphous solid to a flexible polymeric glass. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy () of Ge₂₂Te_78−xI_x glasses at x=5, which is suggestive of a thermally reversing window at this composition.     

Ge1Sb2Te4 Based Chalcogenide Random Access Memory Array Fabricated by 0.18-μm CMOS Technology

Ge1Sb2Te4-based chalcogenide random access memory array, with a tungsten heating electrode of 260hm in diameter, is fabricated by 0.18-μm CMOS technology. Electrical performance of the device, as web as physical and electrical properties of GelSb2 Te4 thin film, is characterized. SET and RESET programming currents are 1.6 and 4.1 mA, respectively, when pulse width is 100 ns. Both the values are larger than those of the Ge2Sb2 Tesbased ones with the same structure and contact size. Endurance up to 106 cycles with a resistance ratio of about 100 has been achieved.     

Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing

Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380℃. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048 MPa. Its bending strength and compressive strength are 529 MPa and 1466 MPa, respectively.     

Superconducting State Parameters of CucZr100-c Binary Amorphous Alloys by Pseudopotential Approach

We present the screening dependence theoretical investigations of the superconducting state parameters, i.e. electron-phonon coupling strength A, Coulomb pseudopotential μ＊, transition temperature To, isotope effect exponent α, and effective interaction strength NoV of some CucZr100-c （C = 25, 30, 33, 35, 40, 45, 50, 55, 57, 60 at.%） binary amorphous alloys by employing the well-known empty core model potential of Ashcroft. Five screening functions proposed by Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. are used to study the screening influence on the aforesaid superconducting properties. The transition temperature Tc obtained from the Ichimaru-Utsumi screening function is found to be in excellent agreement with available theoretical or experimental data. Also, the present results are found in qualitative agreement with the other earlier reported data, which confirms the superconducting phase in the amorphous alloys.     

Thermal Expansion Anomaly and Spontaneous Magnetostriction of Y2Fe14Al3 Compound

The structure and magnetic properties of Y2Fe14Al3 compound are investigated by means of x-ray diffraction and magnetization measurements. The Y2Fe14Al3 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion is found in Y2Fe14Al3 compound in the temperature range from 403 to 491K by x-ray dilatometry. The coefficient of the average thermal expansion is α^- = -2.54Х 10^-5 K^-1. The spontaneous magnetostrictive deformations from 283 to 470 K are caJculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 5.74 × 10^-3 to nearly zero with temperature increasing from 283 to 470K, the spontaneous linear magnetostrictive deformation λc along the c-axis is larger than the spontaneous linear magnetostrictive deformation λa in basal-plane in the same temperature below 350 K.     

Thermally Activated Photoconduction and Alternating-Current Conduction in Se75Ge20Ag5 Chalcogenide Glass: Investigation of Meyer--Neldel Rule

We report on the observation of Meyer-Neldel rule in glassy Se75Ge20Ag5 alloy where AE is varied by two different methods. In the first approach, the intensity of light varies while measuring the photoconductivity in amorphous thin films of Se75Ge20Ag5 instead of changing composition of the glassy system. In the second approach, the variation of ac conductivity with temperature is found to be exponential and the activation energy is found to vary with frequency.     

Thermal Stability of Triangular Ferromagnetic Nanowire Arrays under Magnetic Field

The thermal stability of a triangular nanowire array under an external magnetic field is studied by the damage spreading technique. The results show that stability of the system may be enhanced by decreasing the spacing of magnetic cells (or increasing the storage density). The existence of an external magnetic field is another way to hinder the damage spreading.     

Structural Transition of Gd2O3：Eu Induced by High Pressure

The structural transition of bulk and uano-size Gd2O3：Eu are studied by high pressure energy disperse x-ray diffraction （XRD） and high pressure photoluminescence. Our results show that in spite of different size of Gd2O3 particles, the cubic structure turns into a possible hexagonal one above 13.4 GPa. When the pressure is released, the sample reverses to the monoclinic structure. No cubic structure presents in the released samples. That is to say, the compression and relaxation of the sample leads to the cubic Gd2O3：Eu then turns into the monoclinic one.     

Large relative cooling power of Gd52.5Co16.5Al31 magnetic bulk metallic glass

The magnetocaloric effect and thermal stability have been investigated on the new bulk metallic glass (BMG) Gd_52.5Co_16.5Al₃₁ alloy. The extent of supercooled liquid region is 70 K, which is wider than that of any other Gd-Co-Al ternary BMGs. The magnetic entropy change (ΔS_M) and relative cooling power (RCP) of 9.8 J/kg K and 9.1×10² J/kg are obtained, respectively, under a field change of 5 T. The large ΔS_M and RCP values make Gd_52.5Co_16.5Al₃₁ BMG attractive potential candidate for the magnetic refrigeration application.     

Thermal Diffusivity of Film/Substrate Structures Characterized by Transient Thermal Grating Method

Transient thermal grating method is used to measure the thermal diffusivity of absorbing films deposited on transparent substrates. According to periodically modulated dielectric constant variations and thermoelastic deformations of the thin films caused by the transient thermal gratings, an improved optical diffraction theory is presented. In the experiment, the probing laser beam reflectively diffracted by the thermal grating is measured by a photomultiplier at different grating fringe spaces. The thermal diffusivity of the film can be evaluated by fitting the theoretical calculations of diffraction signals to the experimental measured data. The validity of the method is tested by measuring the thermal diffusivities of absorbing ZnO films deposited on glass substrates.     

Molecular Dynamics Study of Stability of Solid Solutions and Amorphous Phase in the Cu-Al System

The relative stability of fee and bcc solid solutions and amorphous phase with different compositions in the Cu-Al system is studied by molecular dynamics simulations with n-body potentials. For CU1-xAlx alloys, the calculations show that the fee solid solution has the lowest energies in the composition region with x 〈 0.32 or x 〉 0.72, while the bcc solid solution has the lowest energies in the central composition range, in agreement with the ball-milling experiments that a single bcc solid solution with 0.30 〈 x 〈 0.70 is obtained. The evolution of structures in solid solutions and amorphous phase is studied by the coordination number （CN） and bond-length analysis so as to unveil the underlying physics. It is found that the energy sequence among three phases is determined by the competition in energy change originating from the bond length and CNs （or the number of bonds）.     

Nitrogen and Silicon Co-Doping of Ge2Sb2Te5 Thin Films for Improving Phase Change Memory Performance

Electrical properties and phase structures of （Si＋N）-codoped Oe2Sb2Te5 （GST） for phase change memory are investigated to improve the memory performance. Compared to the films with N or Si dopants only in previous reports, the （Si＋N）-doped GST has a remarkable improvement of crystalline resistivity of about 104mΩcm. The Fourier-transform infrared spectroscopy spectrum reveals the Si-N bonds formation in the film. X-ray diffraction patterns show that the grain size is reduced due to the crystallization inhibition of the amorphous GST by SiNx, which results in higher crystalline resistivity. This is very useful to reduce writing current for phase change memory applications.