In-situ electrical resistivity measurements: study of magnetic and phase transitions and solid-HDDR processes in Nd-Fe-B-type alloys

Nd-Fe-B-type alloys have been characterized by means of in-situ electrical resistivity measurements. The potential of this technique for monitoring various phenomena relevant to the hydrogenation, disproportionation, desorption and recombination (HDDR) processing of Nd-Fe-B-type alloys is assessed, together with an evaluation of its capacity for delineating magnetic and phase transitions. The effects of external parameters, such as hydrogen pressure and processing temperature, and of intrinsic parameters, such as alloy composition and initial microstructure, on the kinetics of the solid-HDDR process have been investigated. It was found that the amount of neodymium-rich intergranular phase present in the material had a significant influence on the rates of disproportionation and recombination reactions. At 620C, the recombination process takes place as a solid-solid reaction, and this has a marked effect on the reaction rate. It was also found that the disproportionation process is very sensitive to the hydrogen pressure and the dependence of the overall process on the processing temperature between 620 and 900C has been determined.     

Effect of phase transitions in Fe-Cr-Al alloys on their corrosion resistance in gases and liquid metals

We investigate the process of oxidation of Fe-Cr-Al alloys in argon and liquid sodium at a temperature of 650°C for 1000 h, analyze distinctive features of the process of formation of surface oxide and sub-oxide layers, and demonstrate the effect of phase transitions in alloys on the corrosion losses in these media. The process of oxidation of ferrochrome alloys in the region of homogeneity of -solid solutions in both media results in the formation of oxide layers based on Al₂O₃ on the surface of aluminum-containing alloys. In an atmosphere of argon, the intense growth of the oxide layer promotes the formation of residual stresses followed by its destruction and exfoliation, which leads to an increase in corrosion losses. In liquid sodium, aluminum improves the corrosion resistance of ferrochrome alloys, which is explained both by the suppression of formation of unstable compounds (sodium chromites and ferrates) and the appearance of an interlayer of -phase inclusions between the Al₂O₃ film and the matrix. This interlayer inhibits the growth of the protective oxide layer and enhances its adhesion to the matrix. The -phase is formed in homogeneous ferrochrome -alloys as a result of saturation of their surface layers with carbon present in sodium. If the composition of Fe-Cr alloys is close to equiatomic, their corrosion resistance catastrophically decreases as a result of the bulk transformation which is typical of both media.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 6, pp. 59–66, November – December, 1995.     

电场作用下PVDF薄膜的结构相变与剩余极化特性研究

采用流延工艺制备了半晶态的PVDF薄膜,通过X射线衍射分析（XRD）对不同电场强度下电极化的薄膜进行了表征。电极化的相变过程为α相→δ相→β相。薄膜的铁电性能分析表明,薄膜的剩余极化值Pr随电场强度变化的趋势符合Boltzmann分布函数,拟合的Boltzmann方程表明：引起Pr变化最大的极化电场强度范围是105～125MV／m,最大的剩余极化值Pr达到6μC／cm^2。     

Electrical resistivity and thermoelectric power of copper-germanium films

CuGe films over the whole composition range were prepared by the vapour quenching of the alloys onto glass substrates held at 300 K. The electrical resistivity, thermoelectric power and temperature dependence of the films were studied in the temperature range 100–500 K. The observed behaviour of the electrical resistivity and thermoelectric power is understandable on the basis of transmission electron microscopy and electron diffraction observations which indicate three structural regions. Up to 5 at.% Ge in copper the films are single phase with a structure similar to that of pure copper; in the range 5–80 at.% Ge in copper the films consist of a mixture of Cu₃Ge, copper and germanium; beyond 80 at.% the CuGe films are single-phase amorphous.     

Flux flow resistivity of superconducting thin film

The flux flow resistivity _f has been investigated in the range of reduced temperature 0.5–0.99 for indium thin films having the properties of dirty, type II superconductors. In this temperature range _f was found to show a linear dependence on magnetic field strength for low values of the field. The temperature-dependent viscosity coefficient of the flux flow was obtained and compared with the microscopic theories of Gor'kov and Kopnin (GK) and others. Reasonable agreement with the GK theory was obtained except in the vicinity ofT _c. NearT _c, the viscosity coefficient [in units of ₀H_c(t)_n ^–1c^–2] showed a remarkable decrease beyond a maximum, contrary to the theoretical prediction. Although this behavior is not yet well understood, it seemed to appear asd/ became small. The nonlinearity of the current(I)-voltage(V) curves is also discussed. It was found that a linearI–V curve is found only in the region of temperature and magnetic field where the conditionI _p<1/10I_c is satisfied, whereI _p is the depinning current andI _c is the effective critical current. In the measurements the temperature rise of the film specimens was recorded and the effect due to thermal heating of the specimens was estimated.On leave from Department of Electronic Engineering, Faculty of Engineering, Kyushu Industrial University, Fukuoka, Japan.     

Formation,thermal stability and electrical resistivity of quasicrystalline phase in rapidly quenched Al-Cr alloys

The icosahedral quasicrystal has been found to appear in a wide composition range from about 5 to 16 at % Cr in rapidly quenched Al-Cr alloys, but the formation of the quasicrystal line single phase was limited only in the vicinity of about 15.5at% Cr. Analytical solute concentrations in the quasicrystalline phase are not always constant and increase continuously from 9.0 to 15.4 at% Cr with increasing nominal solute concentration from 6 to 15.4%. The quasicrystal can be approximately formulated to be Al₁₁ Cr₂ with a maximum deviation of about 6% Cr from the stoichiometric ratio to lower concentration side. Vickers hardness and electrical resistivity increase gradually with increasing chromium content and rapidly at about 14.5% Cr, and their values of Al_84.6Cr_15.4 quasicrystal are 710 DPN, 2.38m at 4.2 K, and 2.72m at 293 K. On the other hand, the onset transformation temperature of quasicrystal to crystalline phase,T _t, and the heat of transformation, H _t show maximum values of 644 K and 1805 J mol^–1 at 14.5% Cr and decrease to 625 K and 550 J mol^–1 at 15.4% Cr. Al_84.6Cr_15.4 quasicrystal trans forms at two stages to a stable orthorhombic Al₁₁Cr₂ compound through a metastable intermediate phase with unidentified structure, while the quasicrystal + Al structure in Al-Cr alloys containing less than 15% Cr changes directly to stable phases of compounds and aluminium. The distinct difference in transformation behaviour of the quasicrystal is thought to be the reason for the abrupt changes inT _t and H _t at a composition between 14.5 and 15.4% Cr.     

Anomalous electrical resistivity of thin gadolinium films

Electrical resistivity measurements at room temperature on thin gadolinium films in the thickness range 200–1000 Å are described. The resistivity-thickness curve in this case is anomalous in the sense that it exhibits a decrease in resistivity at lower thicknesses (less than about 500 Å). This is in marked contrast with other work and seems to represent the first observation of a resistivity decrease with decreasing thickness. It is suggested that this curious resistivity characteristic in Gd films results from the thickness dependences of the structural phase and of the spin-disorder resistivity.     

A continuous electrical resistivity measurement in thin films

The continuous electrical resistivity measurement, while an interesting parameter is being changed, can be a useful tool for in-situ thin film analysis as most changes in films are accompanied by changes in the electrical resistivity. In-situ measurements in a tube furnace at atmospheric pressure during different heat treatments are presented for oxidation tracing in Cr films and the TiN/CrN multilayer and for detection of interactions in Ni/Si}, Ti/Si} and Ni/Al multilayers. Results of electrical resistivity measurements c correlated well with weight gain measurements, X-ray diffraction, Rutherford backscattering spectroscopy and Auger electron spectroscopy depth profiling. It is therefore shown that the measurement of the resistivity with its time and temperature derivatives can represent a useful basis for the application of other analytical methods.     

Effect of substrate temperatures on the electrical resistivity of thermally evaporated Mn thin films

Resistivity measurements have been performed on three samples of Mn thin films from 300 to 1.4 K using the van der Pauw four probe technique. The films were grown by thermal evaporation onto glass substrates held at 523, 323 and 77 K, respectively in a bell jar held at 6 × 10⁻⁶ Torr. The resistivity-temperature results of the three specimens reveal a variety of low temperature behaviours. A behaviour typical of the bulk α-Mn is obtained with the film grown at a substrate temperature of 523 K whilst with the film grown at a substrate temperature of 323 K, the resistivity tends to a saturation at low temperatures exhibiting a behaviour reminiscent of Kondo scattering. The resistivity-temperature behaviour of the sample held at a substrate temperature of 77 K may be regarded as typical of a metallic alloy glass with a negative temperature coefficient of resistivity at high temperatures and this turns to a T² dependence of resistivity at very low temperatures.     

Effect of chromium carbides on electrical resistivity of nickel based alloys by low temperature aging

Abstract

To clarify the physical and mechanical properties of nickel based alloys (Alloy 600 and 690), the effects of chromium carbides on the electrical resistivity and hardness were examined after low temperature aging following cold working. In Alloy 600, chromium carbide precipitates were dispersed at grain boundaries and within the grains and the electrical resistivity and hardness increased markedly after short time aging. In Alloy 690, chromium carbides precipitated mainly at grain boundaries and the increases in electrical resistivity and hardness were relatively small, even after long aging times. The most probable mechanism causing the large increases in electrical resistivity in Alloy 600 is the segregation of solute atoms, such as carbon and nitrogen atoms, to dislocation loops around chromium carbides introduced by cold working.

MST/939     

Effect of annealing on the anomalous electrical resistivity of dilute copper-iron alloys at low temperatures

Electrical resistivity measurements in the temperature range 1.5–35 K on two copper alloys containing 115 and 380 atomic ppm iron are reported, in their unannealed state and also after annealing for 16 and 66 h in fore-vacuum at 530–550°C. Below the temperature of the resistivity minimum the impurity resistivity has the Kondo lnT behavior. However, in the liquid helium region the resistivity drops from its value atT=0, in proportion toT ², conforming to Nagaoka's theory forT<T _K/5. The Kondo temperatureT _K is evaluated from the versusT ² plots using Nagaoka's equation and is found to decrease with increasing concentration. Annealing is found to reduce the effective iron concentration and alsoT _K. The impurity resistivity per atomic percent in our samples can be expressed as a universal function ofT/T _K at the lowest temperatures underT _K/4.     

Analysis of the electrical resistivity of double-layer metal film

Assuming that the various sources of scattering act independently in metal films and introducing the mean-free path describing the Fuchs-Sondheimer effect and the grain-boundary scattering, an apparent size effect is defined for a double-layer metal film; a similar method is used for representing any source of scattering with reference to the base layer. General expressions for the electrical conductivity of a double-layer metal film are thus obtained. Qualitative agreement with previous results of other authors is found in the thickness range where these early expressions are valid.     

铅掺杂对BST铁电薄膜性能的影响

为了改善BST铁电薄膜的结晶性能,降低薄膜材料的铁电弛豫和弥散相变特性,采用改进的溶胶-凝胶(sol-gel)方法在Pt/Ti/SiO2/Si基片上制备出了不同铅掺杂的BST薄膜(PBST).研究了PBST薄膜的微观结构及其介电、铁电性能.XRD、AFM分析表明,铅对(101、110)峰的生长促进作用最大,掺入5mol%Pb以上的PBST薄膜的结晶状况得到了明显改善;铅的引入使晶粒增大,降低了薄膜的频率色散现象,相变温区有不同程度紧缩;薄膜的介电、铁电性增强.PBST(0.80/0.20/0.05)薄膜具有适当的相变温区、合适的Tmax值、较小频率色散及比BST薄膜更为明显的介电峰与铁电性等特征,可以作为UFPA系统的探测材料.     

Temperature dependence of electrical resistivity and microstructure of Pb-Cd alloys

The electrical resistivity of Pb-Cd alloys has been studied at various ageing temperatures, for various ageing times. The variations of microstructure with ageing temperature were investigated by scanning and transmission electron microscopy. In addition, the process of coarsening of Pb and Cd ( and phases) at different ageing temperatures was studied by the microanalysis technique. Received 19 October 1990 and accepted 25 March 1991     

Effect of electrical resistivity on ultrasonic attenuation in NpTe

Ultrasonic attenuation due to electron-phonon interaction (EPI) has been computed in semimetallic single crystal neptunium telluride (NpTe) in low temperatures 5-80 K. For the same evaluation, we have also evaluated ultrasonic velocity, electronic viscosity and second order elastic constants (SOEC). The SOEC of NpTe have been evaluated using the Born model of ionic solid. The behaviour of ultrasonic attenuation is quite similar to its inverse resistivity. The ultrasonic attenuation due to EPI is most significant at 40 K. Computed results of ultrasonic parameter have been compared and discussed.     

The electrical resistivity and resistance-temperature characteristics of thin titanium films

In this communication are described the results on the electrical resistivity and resistance-temperature characteristics of titanium films, measured in vacuum. They were evaporated onto soda glass microscope slides at room temperature in a sputter-ion pumped glass belljar vacuum system at about 5×10^-8 torr. The films varied in their thickness from 50 to 1100 Å, and the resistivity was very high for the thinnest films but for the thickest ones it approached approximately double the bulk value. The measured resistivities for the continuous freshly prepared films are too high to be explained on the basis of the Fuchs-Sondheimer theory^{1, 2} for diffuse scattering, and are attributed to porosity and the gaseous impurities taken down during and after their formation. The temperature coefficient of resistance (TCR) was negative for films less than 50–60 Å thick but positive for thicker ones. A bulk mean free path of 285 Å in titanium was calculated at room temperature.     

制备工艺对PAR电双稳薄膜电特性的影响

采用真空蒸发的方法将有机电双稳材料PAR制成Al/PAR/Al夹层结构.详细研究了薄膜厚度、电极面积、退火处理和自然放置等因素对薄膜电性能的影响.结果表明,采用适当的工艺,能够获得性质均匀、电特性良好的电双稳薄膜(转变电压的分散性小于10%,延迟时间基本小于5μs,转变时间在20ns左右).Al/PAR/Al结构可以简单等效为电阻与电容的并联,而退火与自然放置将使薄膜结构趋于稳定.