Thermal Stability Of Amorphous State Research Articles

Effects of rare-earth element Y content on the microstructure and properties of quinary Al–Ni–Zr–Co–Y high entropy metallic glasses

A series of quinary (Al1/4Ni1/4Zr1/4Co1/4)100-xYx (x = 16–28 at.%) high entropy metallic glass ribbons were successfully fabricated through the high-speed single roller melt-spinning method. The effects of rare-earth element yttrium content on the microstructure and performances of alloy ribbons were systematically investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), heat treatment, transmission electronic microscopy (TEM), atomic force microscopy (AFM) and electrochemical experiments. The microhardness of metallic ribbons was measured by Vickers hardness tester. Results show that the microstructure of the as-quenched alloy ribbons maintain the glassy state and the average microhardness value of each specimen can reach 488 HV0.1 or above. The surface morphologies of the as-spun ribbon samples exhibit the smooth surface with small roughness value of Ra = 0.115–0.150 nm. In the meantime, with the increase of Y content, the glass transition temperature can be detected in the DSC traces when Y content is over 22 at.%, and the crystallization onset temperature shifts to the lower temperature region, suggesting that the thermal stability of amorphous state in Al–Ni–Zr–Co–Y alloy ribbons has been weakened. The (Al1/4Ni1/4Zr1/4Co1/4)84Y16 alloy ribbons own the highest crystallization onset temperature (∼742 K). Adding appropriate yttrium element can enlarge the super-cooled liquid region and improve the glass-forming ability. In 3.5 wt% NaCl solution, the prepared alloy ribbons can maintain smaller corrosion current densities (∼10−8 A cm−2) than traditional Al-based amorphous alloys, 6061 Al alloy and other common structural steels. The X-ray photoelectron spectrometer results indicate that the passive film of equiatomic alloy ribbons is rich in oxides of Al, Zr, Co, and Y elements, which has excellent resistance to chloride ion attack. On the basis of all experimental results, (Al1/4Ni1/4Zr1/4Co1/4)84Y16 alloy ribbons can optimally combine outstanding corrosion resistance, superior thermal stability, and acceptable microhardness. The above research results lay a solid foundation for the composition development of high-performance high entropy metallic glasses.

Insulator–metal transition and ultrafast crystallization of Ga40Sb60/Sn15Sb85 multiple interfacial nanocomposite films

The phase change behavior of Ga40Sb60/Sn15Sb85 multiple interfacial film was studied systematically for its application in phase change memory. The thermal stability of amorphous state was evaluated using the Arrhenius formulas. The evolution of phase structure indicates that the Sb phase exists in the Sb-rich Ga40Sb60/Sn15Sb85, Ga40Sb60 and Sn15Sb85 films. The change in density and thickness during crystallization was obtained by X-ray reflectance. The nanoscale change in roughness of the Ga40Sb60/Sn15Sb85 film was confirmed by atomic force microscopy. The rate for crystallization and amorphization transformation was measured by a picosecond laser pump-probe system. The phase change memory device based on [Ga40Sb60 (7 nm)/Sn15Sb85 (3 nm)]5 thin film was fabricated. An ultra-fast switching and low power were achieved for Ga40Sb60/Sn15Sb85 multiple interfacial film.

Effect of Y addition on crystallization behavior and soft-magnetic properties of Fe78Si9B13 ribbons

A series of amorphous Fe-Si-B ribbons with various Y addition were prepared by melt-spinning. The effect of Y addition on crystallization behavior, thermal and magnetic properties was systematically investigated. With the increase of Y content, the initial crystallization temperature shifted to a higher temperature, indicating that the thermal stability of amorphous state in Fe-Si-B-Y ribbon is enhanced compared to that of Fe-Si-B alloy. Meanwhile, compared to the two exothermic peaks in the samples with lower Y content, a new exothermic peak was found in the ribbons with Y content higher than 1at%, which corresponded to the decomposition of metastable Fe3B phase. Among all the alloys, Fe76.5Si9B13Y1.5 alloy exhibits optimized magnetic properties, with high saturation magnetization Ms of 187emu/g and low coercivity HcJ of 7.6A/m.

The Effects of High Magnetic Field Annealing on the Structural Relaxation of Fe71(Nb0.8Zr0.2)6B23 Bulk Metallic Glass

Fe-based magnetic metallic amorphous and nanocomposites have excellent soft magnetic properties including greater magnetization and magnetic permeability compared with crystalline alloys, especially at high operation frequency and temperature. The high magnetic field (HMF) up to 12T is introduced to the heat annealing of Fe71(Nb0.8Zr0.2)6B23 bulk metallic glass (BMG). The 12T HMF annealing shows the effect of improve the thermal stability of amorphous state during annealing in the BMG's supercooled liquid region as compared with the annealing without magnetic field. The HMF annealing inhibits the brittleness of BMG during the structural relaxation, due to the increment of the activation energy under the HMF. The HMF annealing also results in squared hysteresis loops after the structural relaxation and lower coercivity.

Microstructure and Crystallization Kinetics Analysis of the (In15Sb85)100−xZnx Phase Change Recording Thin Films

The (In15Sb85)(100-x)Zn(x) films (x = 0 - 17.4) were deposited on nature oxidized Si wafer and glass substrate at room temperature by magnetron co-sputtering of Sb target and InZn composite target. The thermal property of the films was examined by a homemade reflectivity thermal analyzer. Microstructures of the films were analyzed by transmission electron microscope (TEM). We examined the effects of Zn addition on the thermal property, crystallization kinetics, and crystallization mechanism of the In15Sb85 recording film. As x = 0 - 17.4, thermal analysis shows that the (In15Sb85)(100-x)Zn(x) films have two phase transition temperature ranges which are 189 degrees C-215 degrees C and 300 degrees C-350 degrees C. It is found that the activation energy is increased with Zn content. This indicates that the thermal stability of amorphous state is improved by doping Zn. The optical contrasts of the films are all larger than 15%, as x = 0 - 6.2, indicating that the films have the potential in blue laser optical recording media application.

N-doped Sb 2Te phase change materials for higher data retention

Crystallization temperatures of the Sb 2Te films increase remarkably from 139.4 °C to 223.0 °C as the N 2 flow rates increasing from 0 sccm to 1.5 sccm. Electrical conduction activation energies for amorphous and crystalline states increase by doping nitrogen. A small amount of nitrogen atoms can locate at interstitial sites in the hexagonal structure, generating a strain field, and improving the thermal stability of amorphous state. The best 10-years lifetime at temperature up to 141 °C is found in Sb 2TeN 1 films. Doping excessively high nitrogen in Sb 2Te film will form nitride and make Te separate out. As a result, the activation energy for crystallization decreases instead, accompanying with the deterioration of thermal stability. The power consumption of PCRAM test cell based on Sb 2TeN 1 film is ten times lower than that of PCRAM device using Ge 2Sb 2Te 5 films.

Phase Transition Behaviors of AgInSbTe-SiO2 Nanocomposite Thin Films for Phase-change Memory Applications

AbstractPhase-change kinetics, structure evolution and feasibility to phase-change memory (PCM) of Ag2In7Sb64Te27 (AIST) and its nanocomposite comprised of 85 wt.% AIST and 15 wt.% SiO2 were presented. In-situ heating x-ray diffraction (XRD) indicated nanocomposite transforms from amorphous to HCP structure during heating and incorporation of SiO2 increases the recrystallization temperature (Tx) of samples (189°C for AIST and 223°C for nanocomposite). XRD and transmission electron microscopy (TEM) analyses both revealed the grain refinement in nanocomposite. Kissinger's analysis found the increase of activation energy (Ea) of phase transition in nanocomposite, denoting the SiO2 embedment restrains the grain growth of AIST during recrystallization. Johnson-Mehl-Avrami (JMA) theory revealed the decrease of Avrami exponent (n), indicating that the phase transition is prone to be heterogeneous since the dispersed SiO2 particles may provide additional nucleation sites.Static I–V measurement indicated that the switching threshold voltage (Vth) of nanocomposite device (1.65 V) is higher than that of the AIST device (1.10 V). Increase of dynamic resistance in nanocomposite device leads to the reduction of writing current. I–V analysis also confirmed the retardation of recrystallization in AIST due to the incorporation of SiO2 and the rise of Ea is able to enhance the thermal stability of amorphous state in PCM devices.

Effects of nitrogen doping on the properties of Ge 15Sb 85 phase-change thin film

The effects of nitrogen doping on the chemical bonding state, microstructure, electrical property and thermal stability of Ge 15Sb 85 film were investigated in detail. The doped N atoms tend to bond with Ge to form Ge 3N 4, as proved by X-ray photoelectron spectroscopy analyses. X-ray diffraction patterns showed that both undoped and N-doped Ge 15Sb 85 films crystallize into a hexagonal phase very similar to Sb. The thickness reduction upon crystallization for undoped and N-doped Ge 15Sb 85 films is less than 5%. The crystalline resistivity, crystallization temperature, and thermal stability of amorphous state all increase after nitrogen doping, while the grain size decreases. By adding 7.0 at.% N into the Ge 15Sb 85 film, the crystalline resistivity increases twelve times and the crystallization temperature increases about 50 °C. The maximum temperature for 10-year retention of amorphous Ge 15Sb 85 film is estimated to be 147 °C and that of N-doped films is even higher, which will promise better data retention of phase-change random access memory especially in the high-temperature application.

Optical properties of nanostructure (In15Sb85)100–xZnx thin films

AbstractThe (In15Sb85)100–xZnx films (x = 0∼13.7) were deposited on nature oxidized Si wafer at room temperature by dc co‐sputtering of Sb target and InZn composite target. Effects of Zn content on the optical properties of (In15Sb85)100–xZnx film were examined by X‐ray diffraction and reflectivity thermal analyzer. It is found that the crystallization activity energy of the film is increased with Zn content, this indicates that the thermal stability of amorphous state is improved by doping Zn. The structure of as‐deposited (In15Sb85)100–xZnx film was amorphous and it would transform to Sb, InSb, and ZnSb coexisting phases after annealing at 250 °C. The reflectivity of annealed film was higher than that of as‐deposited film. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electroless deposition and some properties of Ni–Cu–P and Ni–Sn–P coatings

In this review, a summary of our published results, completed with new unpublished data are considered together with some of other authors’ publications, making an attempt to reveal the mechanism of the third element co-deposition in electroless Ni–P plating and to define its influence on the ternary coatings’ properties. A model explaining the triple role of Cu added to the solution for electroless (EL) Ni–P plating is described: as a stabilizer [Cu(I)]; as an accelerator; and as a stability-affecting agent, forming a dispersed solid phase in the solution. The disproportionation reaction of Cu(I) has been taken into account. A planned experiment was performed using full-effect factorial design with two levels of three process variables, and the response surfaces were constructed. The interaction between the factors was revealed. The results are in harmony with the aforementioned model. In low-tin Ni–Sn–P coatings, the alloy components are uniformly distributed both on the surface and through the thickness. In contrast, high-tin coatings exhibit three-dimensional areas enriched in Sn and impoverished in Ni and P. As the reason for their formation, the disproportionation reaction of Sn(II) is suggested, supposed to be locally predominant over the hypophosphite oxidation. EL deposition of pure Sn onto Ni–Sn–P substrates is shown. The inclusion of Cu or Sn in EL Ni–P increases the thermal stability of amorphous state, ensures the preservation of a paramagnetic behavior and improves the corrosion resistance.