The electrical resistivity of amorphous alloys at low temperatures

Measurements of the temperature- and magnetic field dependence of the electrical resistance of some metallic glasses are presented. The data obtained for Cu₅₇Zr₄₃, Cu₄₀Zr₆₀ and Pd₃₀Zr₇₀ demonstrate that deviations from the high temperature behaviour extrapolated to low temperatures are caused by superconducting effects. The paraconductivity which is strongly enhanced in amorphous alloys is shown to agree quite well with theoretical models. The normal state resistance does not saturate down to temperatures of about 2 K. It still exhibits a negative temperature coefficient of the resistivity.     

Low-temperature properties of ordered Cu<Subscript>3</Subscript>Pd-based alloys

The effect of atomic disordering and alloying with d elements (Fe, Pd, Cu) on the transport and magnetic properties of Cu₃Pd alloys has been investigated at low temperatures (T < 80 K) in strong magnetic fields (H ≤ 8 MA/m). The specific features of the crystal structure and temperature and field dependences of the electrical resistance, magnetoresistance, Hall effect, and magnetic susceptibility of Cu₇₂Pd₂₈, Cu₇₅Pd₂₅, Cu₈₀Pd₂₀ and Cu_74.5Pd_24.5Fe₁ alloys are discussed.     

Hydrogen depth profile in sputtered CuxZr1-x amorphous alloys studied by nuclear reaction analysis. Evolution as a function of annealing temperature.

Hydrogen depth profiles in thin films of sputtered Cu_xZr_1-x amorphous alloys have been measured using the resonant nuclear reaction ¹H (¹⁵N, αγ)¹²C. In Cu_0.3Zr_0.7, Cu_0.4Zr_0.6 and Cu_0.5Zr_0.5 alloys the hydrogen bulk concentrations expressed bythe atomic ratio H/Zr are respectively 0.26, 0.45 and 0.80. Hydrogen mobility under beam impact is observed at both interfaces (air-film, film-substrate) and in the molybdenum substrate. Evolution of the hydrogen profiles has been followed as a function of annealing temperature. No departure of hydrogen is observed below 520K; at temperatures close to the crystallisation, the hydrogen content remains high, in the 20–30 at % range. These results are discussed in correlation with physical properties of the alloys.     

Magnetic interference effect in amorphous D-band metals with high electrical resistivity

Systematic occurence of low temperature resistivity anomalies (upturn) in amorphous alloys Zr₅₀Cu₅₀, Zr₇₅Ni₂₅, and Y₇₅A?₂₅ containing up to 4 at .% Gd is observed. Detailed analysis of ‘background’ impurity (other than Gd) effects on the electrical resistivity of the alloy host Zr₅₀Cu₅₀ provides unambiguous evidence that the anomalies are due solely to the Gd ions. The present results are interpreted in terms of conduction electrons with short mean free path scattering from nearest neighboring pairs of Gd spins. Predictions derived from the diffraction type model of magnetic interference, however, fail to describe all the results on metals with high electrical resistivity. Data on Zr₅₀Cu₅₀ containing Fe and Mn are also discussed.     

Acid corrosion of amorphous and crystalline Cu-Zr alloys

Corrosion resistance of amorphous and crystalline Cu₄₅Zr₅₅, Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ alloys in strong acid (C_H⁺ = 1 M ℓ^-1) solutions was investigated with the use of potentiodynamic and gravimetric techniques. It was observed that the corrosion resistance of these alloys tested in H₂SO₄ and HNO₃ solutions was very high. However, amorphous Cu-Zr alloys exhibit a lack of resistance in HCl solutions where the corrosion rate increases with the rise of Cu content in the alloy (selective etching of Zr). Crystallization of alloys strongly improves their resistance to corrosion in HCl provided the Zr content in an alloy ⩾ 50 at%.     

The characterisation of atomic structure and glass-forming ability of the Zr–Cu–Co metallic glasses studied by molecular dynamics simulations

In the present work, the glass formation process and structural properties of Zr₅₀Cu_50-xCo_x (0 ≤ x ≤ 50) bulk metallic glasses were investigated by a molecular dynamics simulation with the many body tight-binding potentials. The evolution of structure and glass formation process with temperature were discussed using the coordination number, the radial distribution functions, the volume–temperature curve, icosahedral short-range order, glass transition temperature, Voronoi analysis, Honeycutt–Andersen pair analysis technique and the distribution of bond–angles. Results indicate that adding Co causes similar responses on the nature of the Zr₅₀Cu_50-xCo_x (0 ≤ x ≤ 50) alloys except for higher glass transition temperature and ideal icosahedral type ordered local atomic environment. Also, the differences of the atomic radii play the key role in influencing the atomic structure of these alloys. Both Cu and Co atoms play a significant role in deciding the chemical and topological short-range orders of the Zr₅₀Cu_50-xCo_x ternary liquids and amorphous alloys. The glass-forming ability of these alloys is supported by the experimental observations reported in the literature up to now.     

Structural transformation studies on the rare earth containing Heusler alloys Pd2RESn

The Heusler alloys Pd₂RESn form for rare-earths (RE) from Tb to Lu and for Sc and Y. Of these, the alloys containing Yb, Tm, Lu, Sc and Y are superconducting. We have carried out structural studies on all these alloys by studying the temperature dependence of the X-ray patterns in the temperature range 5 to 300 K. Some nonstoichiometric compositions were also investigated. Structural transformation is observed only in Tb and Dy containing alloys while none of the superconducting alloys show a transformation. The transformation temperature is lowered by about 50 K in going from stoichiometric Pd₂TbSn to nonstoichiometric Pd₂Tb_0.95Sn while it is completely suppressed in Pd₂Dy_0.95Sn. Magnetic and Mössbauer studies on Dy compound are also reported.     

Electrical resistivity of ternary glassy and liquid Pd-alloys

The electrical resistivity of liquid (Pd₁₀₀Cu_100?x)₈₀Ge₂₀ alloys has been measured as a function of temperature. For Cu-rich negative temperature coefficients and for Pd-rich alloys positive temperature coefficients of the electrical resistivity have been observed. This behavior is very similar to recent observed resistivity temperature curves of glassy (Pd₁₀₀Cu_100?x)₈₀P₂₀ alloys. An explanation of the resistivity behavior in terms of liquid metals theory is suggested.     

Effect of Fe on the glass-forming ability,structure and devitrification behavior of Zr–Cu–Al bulk glass-forming alloys

We report on the glass-forming ability and devitrification behavior of Zr₆₀Cu₃₀Al₁₀, Zr₆₀Cu₂₅Al₁₀Fe₅ and Zr_62.5Cu_22.5Al₁₀Fe₅ bulk glass-forming alloys on heating. The effect of Fe addition on the structure of Zr–Al–Cu alloys is also discussed. Crystallization kinetics and structural changes in the glassy alloys were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The results indicate that good glass-formers, such as Zr_62.5Cu_22.5Al₁₀Fe₅, are located somewhat beyond the equilibrium eutectic point. Possible phase separation in the supercooled liquid on heating and electron beam-induced in situ crystallization are observed and discussed.     

Photoemission study of Pd Zr and Cu Zr alloys

The XPS valence bands and core levels of the alloys Pd_1?xZr_x (0<x<1) and Cu_1?xZr_x (0<x<1) have been measured. The alloys prepared by coevaporation are crystalline — but their valence band spectra are close to those of the metallic glasses of the same compositions. The large valence band and core level shifts observed for Pd can be explained by a simple theory, not necessitating the postulation of a new type of bonding in these systems.     

非晶态Cu56Zr44合金的结构及其等温退火晶化过程的研究

利用X射线衍射技术、差示扫描量热分析技术和透射电子显微镜研究了非晶态Cu₅₆Zr₄₄合金的结构及其等温退火条件下的晶化过程.实验结果表明,非晶态Cu₅₆Zr₄₄合金在室温下的短程结构类似于硬球无规密堆积分布.在703K过冷液相区内等温退火时发现,当退火时间为3min时,晶化产物主要为Cu₈Zr₃相;当退火时间为6min时,Cu₈Zr₃关键词： 非晶态 56Zr₄₄合金')" href="#">Cu₅₆Zr₄₄合金 结构 等温退火     

Positron lifetime measurements on electron irradiation damage in amorphous Pd80Si20 and Cu50Ti50 alloys

Positron lifetime measurements were performed on amorphous Pd₈₀Si₂₀ and Cu₅₀Ti₅₀ alloys irradiated with 3MeV electrons at 20K. The irradiation was found to increase the mean positron lifetime in both specimens indicating the presence of vacancy-like radiation damage. Isochronal annealing between 77 K and 300 K resulted in a continuous reduction of the positron lifetime, which suggests a gradual recovery of the irradiation induced defects.     

Acoustic experiments on amorphous Pd30Zr70 and Cu30Zr70 in the superconducting and the normal state

Measurements of internal friction and sound velocity of amorphous Pd₃₀Zr₇₀ and Cu₃₀Zr₇₀ around 1 kHz and of Pd₃₀Zr₇₀ around 1 GHz are presented for both the superconducting and the normal state. Our experiments reveal several serious discrepancics with the predictions of the Tunneling Model and its extension to metallic glasses. Particularly from internal friction we conclude that the density of states of the tunneling systems is affected by the presence of conduction electrons. We discuss our results on the basis of recent theories which consider a slowing down of the tunneling motion due to the interaction with conduction electrons.Dedicated to K. Dransfeld on the occasion of his 60th birthday     

Enhancement of thermopower in the highT c superconductor YBa2Cu3O7 and related compounds

The absolute thermopower of single phase YBa₂Cu₃O₇ and Y_0.8Er_0.2Ba₂Cu₃O₇ has been measured in the range 250 K to the superconducting transition temperature. It is found that these compounds show a large enhancement of thermopower in the range 150 K down toT _c. This enhancement shows a steep exponential drop as the temperature increases from the transition temperature. The temperature variation of the enhancement is too steep to be accounted for by electron-phonon or electron-local structural excitation mechanisms.     

On the level of mechanical loss in metallic glasses

Metallic glass samples with compositions Zr₆₅Al_7.5Cu_27.5 and Pd₇₇Cu₆Si₁₇, for which loss factors of up to 10^-2 have been reported, are reinvestigated with an electrostatic vibrating cantilever technique that detects dissipation factors tan δ as low as 10^-4. It is found that tan δ ≈ 4×10^-4 is a typical value for these alloys well below T _g , suggesting that previous results were limited by instrumental resolution. While aging the glasses increases their elastic moduli considerably, the measured loss factor is affected only marginally by thermal history.     

AgxCu50-xZr50非晶态合金及其晶化

采用高频熔炼后的真空单辊急冷技术制备了Ag_xCu_50-xZr₅₀金属玻璃,发现在x<12的范围内都可得到完全的非晶态。测量了x=2,4,6和10的Ag_xCu_50-xZr₅₀金属玻璃的玻璃转变温度和晶化温度,并采用Kissinger方法测定了晶化激活能E_a。发现在金属玻璃Ag_xCu_50-xZr_{50关键词：}     

Manifestation of anharmonic localized vibrational modes in the specific heat and vibrational spectrum of freshly prepared amorphous alloys

The low-temperature specific heat of freshly prepared and annealed amorphous alloys Zr₇₀Be₃₀, Zr₆₇Cu₃₃, and Zr₇₅Rh₂₅ has been investigated experimentally. The integral parameters of the electronic and phonon spectra have been determined: the Sommerfeld coefficients and the Debye temperatures. Data from calorimetric and neutron experiments were compared on the basis of the theory of lattices with off-diagonal disorder and localized modes. It is concluded that a local rearrangement of the structure occurs in freshly prepared samples as the temperature decreases. A model of a bistable impurity configuration is proposed to explain this restructuring. Fiz. Tverd. Tela (St. Petersburg) 39, 145–152 (January 1997)     

基于成分连续变化计算黏度的合金系临界冷速模型

在大块非晶临界冷却速率的非等温转变计算模型基础上提出了基于成分连续变化计算黏度的合金系临界冷速模型. 依据此模型对Zr-Ni-Al-Cu四元合金的临界冷却速率进行了计算并预测了Zr_66.67(Ni_{xAlyCuz)33.33合金系中容易形成非晶的成分范围. 计算值与实验值符合得较好. 计算结果表明，此合金系具有很强的非晶形成能力，特别是在靠近共晶点的中心区域，临界冷却速率小于100 K/s，为容易形成非晶的成分范围. 冷却过程中，在高于1000K温度区间，没有发生明显的结晶现象，而在980 K至870 K温度范围内，结晶分数快速增大，低于870 K时不再发生明显改变. 此外，分析了合金系中Al，Cu，Ni原子摩尔分数的变化对临界冷速的影响. 关键词： 大块非晶 黏度 临界冷却速率 非晶形成能力}     

Magnetic behavior of amorphous Fe−Ni−Zr alloys and their response to radiation damage

The magnetic properties of two amorphous Fe?Ni?Zr alloys, Fe_89.7Ni_0.03Zr₁₀ and Fe₇₀Ni₂₀Zr₁₀, both in the “as cast” and neutron irradiated states were investigated by Mössbauer spectroscopy and dc magnetic susceptibility measurements. The upper magnetic ordering temperatures of Fe_89.7Ni_0.03Zr₁₀ are 232K and 246K for the “as cast” and irradiated samples, respectively. The magnetic ordering temperature for Fe₇₀Ni₂₀Zr₁₀ was about 478K for both the “as cast” and irradiated samples. Both compositions yield magnetic hyperfine spectra, which show a considerable relaxation effect that must be explicitly considered in the calculation of the average local Fe moments. When this is done, these values derived from Mössbauer spectra are in good agreement with the dc susceptibility values. The effects of neutron irradiation on the magnetic properties of these alloys are small.     

Susceptibility of crystalline alloys to deformational amorphization during torsion under quasi-hydrostatic pressure

Features of the transition of Ni₅₀Ti₃₀Hf₂₀, Ti₅₀Ni₂₅, Zr₅₀Ni₁₈Ti₁₇Cu₁₅, and Fe₇₈B_8.5Si₉P_4.5 crystalline alloys with different susceptibilities to amorphization upon annealing and in the amorphous state during intense deformation in a Bridgman chamber are considered. The single- and two-phase crystalline states of the chosen alloys are obtained in different annealing modes. It is shown that the amorphizing rate of crystalline alloys differ substantially at the same degree of deformation; i.e., single-phase crystalline alloys based on titanium nickelide and iron amorphize well, while zirconium-based alloy amorphizes weakly in a manner similar to two-phase iron alloy. We believe that the LDA of crystalline alloys and their corresponding crystalline phases is determined by mechanical, thermodynamic, and concentration factors.