Preparation of nickel-based amorphous alloys with finely dispersed lead and lead-bismuth particles and their superconducting properties

The application of the melt-quenching technique to Ni-Si-B-Pb, Ni-P-B-Pb, Ni-Si-B-Pb-Bi and Ni-P-B-Pb-Bi alloys containing immiscible elements such as lead and bismuth has been tried and it has been found to result in the formation of a new type of material consisting of fine fcc Pb or hcp (Pb-Bi) + bct X(Pb-Bi) particles dispersed uniformly in the nickelbased amorphous matrix. The particle size and interparticle distance were 1 to 3 and 1 to 4 µm, respectively, for the lead phase, and less than 0.2 to 0.5 µm and 0.2 to 1.0 µm for the Pb-Bi phase. The uniform dispersion of such fine particles into the amorphous matrix was achieved in the composition range below about 6at% Pb and 7at% (Pb + Bi). Additionally, these amorphous alloys have been found to exhibit a superconductivity by the proximity effect of f c c Pb or (Pb-Bi) superconducting particles. The transition temperatureT _c was in the range 6.8 to 7.5 K for the Ni-Si(or P)-B-Pb alloys and 8.6 to 8.8 K for the Ni-Si (or P)-B-Pb-Bi alloys. The upper critical fieldH _c2 and the critical current densityJ _c for (Ni_0.8 P_0.1 B_0.1)₉₅ Pb₃ Bi₂ at 4.2 K were, respectively, about 1.6T and of the order of 7 X 10⁷ A m^–2 at zero applied field. Melt quenching of amorphous phase-forming alloys containing an immiscible element has thus been demonstrated, enabling us to produce amorphous composite materials exhibiting unique and useful characteristics which cannot be obtained in homogeneous amorphous alloys.     

Microstructure and superconducting properties of melt-quenched insoluble Al-Pb and Al-Pb-Bi alloys

In order to obtain aluminium-based superconducting alloys including finely dispersed lead or Pb-Bi particles, the application of the melt-quenching technique has been tried for Al-Pb, Al-Si-Pb and Al-Si-Pb-Bi alloys containing immiscible elements such as lead and bismuth. It has been found to result in the preparation of superconducting materials consisting of fcc Pb or h c p (Pb-Bi) particles dispersed finely and densely in the aluminium-based matrix in each composition range below about 2 at % Pb for Al-Pb alloys and 5 at % Pb or (Pb + Bi) for (Al_0.9 Si_0.1)_100–x Pb _x and (Al_0.9Si_0.1)_100–x (Pb_0.6Bi_0.4) _x alloys. The particle size and interparticle distance were 40 nm and 40 to 100 nm, respectively, within the grains, and 100 nm and below 30 nm, respectively, at the grain boundaries for the lead phase in Al₉₈ Pb₂ alloy. Particle size was 15 to 60 nm and interpartide distance 30 to 60 nm for the Pb- Bi phase in (Al_0.9 Si_0.1)₉₅(Pb_0.6 Bi_0.4)₅ Transition temperature,T _c was 4.16 K for Al₉₈Pb₂, 3.94K for (Al_0.9Si_0.1)₉₅ Pb₅ and 7.75 K for (Al_0.9Si_0.1)₉₅(Pb_0.6Bi_0.4)₅. The upper critical magnetic field,H _c2, and critical current density,J _c, for (Al_0.9Si_0.1)₉₅(Pb_0.6Bi_0.4)₅ were 0.22 T at 4.2 K and 1.67 × 10⁷ Am^–2atzeroappliedheld and 4.2 K. The appearance of the superconductivity for the aluminium -based alloys was interpreted as due to the formation of superconducting percolation path along the tangled dislocations, sub-boundaries and/or grain boundaries where Pb and Pb-Bi phases precipitated preferentially.     

Anomalous electrical resistive behaviour of Al-O-Pb sputtered alloys

Application of the sputtering technique to (Al-O) _x Pb_100-x alloys containing an immiscible lead element has been found to result in the formation of a duplex material consisting of f cc lead particles dispersed in an amorphous Al _x O _y oxide matrix. The particle size and interparticle distance of the lead phase were about 10 to 50 nm and 10 to 40 nm, respectively. The Al-O-Pb alloys have been found to exhibit an extremely high electrical resistivity (), e.g., 4.06 x 10⁶ cm for (Al-O)_87.5 Pb_12.5 at 273 K, as well as a large positive temperature-dependent resistivity reaching 92% Of 273. The peculiar resistivity behaviour was interpreted by assuming the mechanism that only the lead phase embedded in Al_xO_y matrix contributes to electrical conductivity and the mobility of lead electrons is greatly reduced in the intervening oxide region among lead phases. It has thus been demonstrated that the composite material exhibiting peculiar characteristics, which cannot be achieved in metallic composite materials, is obtained by simultaneously sputtering oxide and an insoluble metallic element.     

High-field superconductivity in Al-O-Pb and Al-O-Pb-Bi sputtered films

The sputter-quenched Al _x O _y alloys containing lead and bismuth elements, which are insoluble to aluminium; have been found to exhibit a remarkably enhanced upper critical field,H _c2, which is higher by about 6 to 66 times than those of pure lead metal and Pb₆₀Bi₄₀ alloy. The sputtered structure consists of amorphous Al _x O _y and f c c lead or h c p (lead-bismuth) phases. The lead and phases disperse homogeneously in the amorphous matrix and their particle sizes and interparticle distances are about 10 to 20 nm and 5 to 20 nm, respectively, for lead and particles. The superconducting transition temperature,T _c, upper critical magnetic field,H _c2, at 4.3 K, and residual resistivity at 10 K are 7.74 K, 3.3 T and 2.09 × 105cm, respectively, for (Al-O)_92.8 Pb_7.2 and 7.45 K, 8.2 T and 1.70 × 106 cm, respectively, for (Al-O)_86.2(Pb_0.6 Bi_0.4)_13.8. The remarkable enhancement ofH _c2 is interpreted as being mainly due to a remarkable decrease of the coherence length resulting from a large reduction of the effective mean free path of electrons. Additionally, the fluxoid pinning force under applied field has also been markedly enhanced for the duplex structure films than for sputtered lead film, probably because of the change of the dispersed lead phase into a type-II superconductor and an effective fluxoid pinning action at the interface between Al _x O _y and fine lead particles.     

The effect of particles on the critical strain associated with the Portevin-LeChatelier effect in aluminium alloys

The effect of particles on the critical strain, _c, associated with the Portevin-LeChatelier (PL) effect of aluminium alloys is studied using Al-Mg-Ni and Al-Si alloys. Al-Mg-Ni and Al-Si alloy matrixes are composed of Al₃Ni and Si particles, respectively. Tensile tests were performed in the temperature range 223–273 K in which the critical strain decreases with increasing temperature, and strain rates between 10^–5 and 10^–2 s^–1 were chosen. According to the apparent activation energies, Q, Mg and Si solute atoms are responsible for the flow instability in Al-Mg-Ni and Al-Si alloys, respectively. The experimental results also show that the critical strain decreases with decreasing particle spacing, d _p. Since the particle spacing is small compared to the corresponding grain size, the decrease in critical strain should be ascribed to the effect of particles. Considering that the dislocation density is increased by the particles, a modified model showing the critical strain, _c, as a function of particle spacing, d _p, is proposed as T ^–1 exp (–Q/kT), in which , T and k are the strain rate, temperature and Boltzmann constant, respectively. Linear fit of the plots of In _c versus In d _p and In _c versus In d _p indicates that this equation is appropriate to rationalize the particle effect on the critical strain.     

Optical and photoelectric properties of Cd<Subscript>1 - <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>As<Subscript>2</Subscript> single crystals

The optical absorption, photoconductivity, and short-circuit photocurrent spectra of structurally perfect Cd_{1 - x} Zn_xAs₂ (x = 0.03, 0.05, 0.06) single crystals are studied for the first time near the intrinsic edge in the range 80–300 K. The results demonstrate that the intrinsic edge in the solid solutions is due to indirect transitions involving the formation of excitons for both the E c and E c polarizations. The indirect gaps _g ⁱ of the solid solutions are determined. In the range 80–300 K, the data for x = 0–0.06 and both polarizations are well fitted by _g ⁱ (x) = _g ⁱ (0) + 0.0866x + 2.35x ². The introduction of 6 mol % ZnAs₂ into CdAs₂ increases its _g ⁱ by 14 meV.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 268–272.Original Russian Text Copyright © 2005 by Morozova, Marenkin, Mikhailov, Koshelev.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Superconducting and electrical properties of amorphous zirconium-transition metal binary alloys

In order to clarify the compositional effect on the superconductivity of zirconium-transition metal (M) binary amorphous alloys, the superconducting properties and electrical resistance of the alloys were examined as functions of the concentration, group number and periodicity of the M elements.T _c for Zr₇₅M₂₅ alloys rises in the order Ru > Rh > Ir > Co > Os > Ni > Pt > Cu > Pd > Fe > Au, i.e. as the group number decreases when the periodicity belongs to the 5th period, and with decreasing M content for Zr_100–X M _X alloys. The highT _c attained in the present work is 4.55 K for Zr₈₀Rh₂₀, 4.38 K for Zr₇₅Rh₂₅ and 4.47 K for Zr₇₅Ru₂₅. The temperature gradient of the upper critical magnetic field (H _c2) near the transition temperature (T _C) tends to increase with increasing zirconium content, and the resistive state due to the flux flow phenomena appears in a wide sweeping field. Following the sharp and large decrease of the flux flow resistance due to a peak effect, the resistance recovers sharply nearH _c2. The peak effect was found to occur more distinctly for the alloys containing a magnetic element of iron or cobalt, probably because of the suppression of the pair-breaking effect due to magnetic scattering by the application of the high field nearH _c2. The dominating factor for the compositional effect onT _C is inferred to originate from the variation of through for Zr_100–x M _X alloys and from that of through N(E_f) for Zr₇₅M₂₅ alloys. Additionally, it has been found for the Zr-M amorphous alloys that the electrical resistivity(T) exhibits a maximum value at temperature ranging from 2T _C to 3T _C, suggesting that the hump phenomenon in (T) appeared through the generation of the superconducting fluctuations. The temperature coefficient of resistivity (tcr) defined by 1/R₂₅₀(dR/dT) shows negative values ranging from 1.05×10^–4 to 1.75×10^–4 K ^–1 andT _C was found to rise through the increase in with the increase in the negative value of the tcr.     

The effect of PbO content on a modified lead titanate ceramic

Modified lead titanate ceramics were prepared from batches with compositions Pb_xCa_0.30Ti₀₉₄ (Co_1/2W_1/2)_0.06O_23+x (x = 0.67, 0.68, 0.69, 0.70, 0.71 and 0.72) with 1 mol % MnO to determine the effect of PbO content on the dielectric and piezoelectric properties. An increase in PbO content increased the grain size and reduced the planar coupling factork _p. The dielectric constant _T ³³ /₀ and the piezoelectric constantd ₃₃ reached a maximum for a ceramic made from a batch with stoichiometric PbO content (x = 0.70).     

The preparation of ductile high strength Fe-base filaments using the methods of glass-coated melt spinning

High toughness glass-coated metallic fibres show great promise for use in composite materials as reinforcement for brittle matrixes such as fine ceramics. This paper describes the glass-coated melt spinning of austenitic steel and Fe-B base alloys in order to prepare a ductile high strength filament. The toughness was estimated from the area of the stress-strain curves of the filament obtained. Continuous high toughness steel filament, which had a maximum toughness of 6600 MPa% with a tensile strength of 3050 MPa and an elongation of 3.1% was obtained from the molten state at 1600 K for a winding speed of 7.95 m sec^–1. The filament was 3×10^–6m diameter and polycrystalline with a grain size of 1000×10^–10m. The crystal structure of the filament was a single b c c phase and the phase transformed into a stable f c c structure by heat treatment at 1073 K for 600sec. Ductile filaments of Fe_78-x Co₅Ni₅Cu₂B₁₀M _x (M _x Cr_5–20, Cr₅Si₃, Cr₅Co₅, Cr₅Ni₅, Cr₁₀Mo_0.5, Cr₁₀Nb_0.5) alloys were also successfully produced. The Fe_67.5Co₅Cr₁₀Ni₅Cu₂B₁₀Mo_0.5 filament had the highest toughness of 13 900 MPa% with tensile strength of 3760 MPa and an elongation of 4.8%. The filament had a single b c c phase.     

Variation of dendrite arm spacing in Al-rich Zn-Al off-eutectic alloys

Primary and secondary arm spacings were measured in various unidirectionally solidified Al-rich Zn-Al off-eutectic alloys. In order to determine the influence of convective processes on dendrite arm spacings, freezing was carried out both vertically upwards and downwards, and over a wide range of growth rates. The primary arm spacing parameter (d ₁) has been correlated with the growth rate (R), the temperature gradient in the liquid immediately ahead of the solid/liquid interface (G _L) and the bulk alloy composition (C ₀). Similar correlations were made for the secondary arm spacing (d ₂). In addition,d ₂ values were found to be related to the local solidification time (t _f). It was observed that the relationshipR ^k G ^m d ₁ =K, the primary arm spacing, andR ^l d ₂ =K, secondary arm spacing, were obeyed (K andK are constants). In addition, the effects of solute gradient-induced convection on the extent of macrosegregation in these alloys have been determined as a function of composition and growth rate.Nomenclature d ₁ Primary arm spacing, m - d ₂ Secondary arm spacing, m - R Growth rate, m sec^–1 - G _L Temperature gradient ahead of the solid/ liquid interface, ° C m^–1 or ° C cm^–1 - C ₀ Bulk alloy composition, wt% - K,K,K Constants - k, m, l, n Exponents - t _f Local solidification time, sec. - T ₀ Freezing interval atC ₀, ° C - L Distance between eutectic front and the plane of dendrite tips, m - r _t Tip radius of dendrites, m - D Diffusion coefficient of solute in the melt, cm²sec^–1 or m²sec^–1 - Gibb-Thomson coefficient, °C. cm or °C m - k ₀ Distribution or partition coefficient - K _T Thermal diffusivity - P _s Solutal Peclet number - P _t Thermal Peclet number - R _t Thermal Rayleigh number     

Mechanical properties of ductile Fe-Ni-Zr and Fe-Ni-Zr (Nb or Ta) amorphous alloys containing fine crystalline particles

Melt-quenched Fe_60–80Ni_10–30Zr₁₀ and Fe₇₀Ni₂₀Zr_10–x (Nb or Ta) _x (x2 at %) alloy ribbons with the duplex structure consisting of amorphous and bcc phases were found to exhibit hardness and tensile strengths higher than those of the totally amorphous alloys. The volume fraction of the bcc phase was intentionally allowed to alter in the range 0% to 60% by changing the composition and sample thickness. The bcc phase has an average particle size of 75 nm for the Fe-Ni-Zr alloys and 50 nm for the Fe-Ni-Zr-Nb alloys, and the lattice parameter is much larger than that of pure -Fe because of the dissolution of large amounts of zirconium, niobium and/or tantalum. The hardness and tensile strength of the duplex alloys increase with amount of bcc phase and reach about 880 DPN and 2580 MPa, which are higher by about 20% to 30% than those of the amorphous single state, at an appropriate volume fraction of bcc phase. As the volume fraction of the bcc phase increases further, the duplex alloys become brittle and the tensile strength decreases significantly. The enhancement of strength was considered to be due to the suppression of shear slip caused by fine bcc particles dispersed uniformly in the amorphous matrix. It was thus demonstrated that an optimum control of melt-quenched structure results in the formation of ductile Fe-based amorphous alloys containing fine crystalline particles.     

Non-equilibrium crystalline superconductors in Zr-Si binary alloys rapidly quenched from melts

The new non-equilibrium superconductor with a b c c structure has been found in rapidly quenched Zr-Si alloys. The silicon content in the b c c alloys was limited to the narrow range between 8 and 11 at%. The b c c alloys showed a superconducting transition whose temperature increased from 3.20 to 3.84 K with decreasing silicon content. The upper critical magnetic field and the critical current density for Zr₉₂Si₈ alloy were of the order of 3.58 × 10⁶ Am^–1 at 2.0 K and 3.3 × 10^–2 Am^–2 at 2.42 K in the absence of an applied field. The upper critical field gradient at the transition temperature and the electrical resistivity at 4.2 K were about — 1.82 × 10^–1 Am^–1 K^–1 and about 150 cm. The Ginzburg-Landau parameter and coherence length _GL (0) were estimated to be about 65 and 6.3 nm, respectively, from these experimental values by using the Ginzburg-Landau-Abrikosov-Gorkov theory and hence it is concluded that the present b c c alloys are extremely soft type-II superconductors with a high degree of dirtiness.     

Microstructural evolution of FINEMET type alloys with chromium: An electron microscopy study

Microstructural changes in Fe_73.5–xCr_xCu₁Nb₃Si_13.5B₉ (0x5) alloys with thermal treatment were studied by electron microscopy. In a first stage, around 800 K, an Fe(Si) nanocrystalline phase is formed in the amorphous residual matrix. Crystallization onset is enhanced with the Cr content of the alloy. In a second stage, around 950 K, full crystallization of the samples leads to the formation of a body centred cubic (b.c.c.) boride-type unknown crystal phase with a lattice parameter of a=1.52 nm, and recrystallization of the previous Fe(Si) nanophase also occurs. No qualitative differences were found between dynamic and isothermal crystallization. The size effect for thin samples is limited to a lowering of crystallization temperatures. For isothermal nanocrystallization in the temperature range 775–900 K, the mean grain size of the nanocrystals increases for short annealing times to stabilize at a constant value of about 10–15 nm for long annealing times. The stabilized grain size increases with increasing annealing temperature and slightly decreases with the Cr content of the alloy.     

Magnetic scattering of conduction carriers in 3d transition-metal intercalates of M x TiS2 (M=Mn,Fe, Co,and Ni)

Galvanomagnetic measurements on layer-structured 3d transition-metal intercalates of M_xTiS₂ (M = Mn, Fe, Co, and Ni;x0.33) have been made over the temperature range 0.34–20 K. Resistivity minima and negative magneto-resistances are observed for paramagnetic Mn, Fe, and Ni intercalates with low guest concentrations (x0.1), as found in well-known dilute alloys. However, in the case of the weak-ferromagnetic phase of Co_xTiS₂ (0.10x0.33) with the Curie temperatureT _c =120–140 K, such anomalous behaviors are also observed, which is not commonly found in the magnetically ordered phases of various magnetic materials. With these data we have given qualitative discussions on the magnetic scattering process of conduction carriers. Further, some of the experimental results are discussed in connection with the band calculations for M_1/3TiS₂.     

Structure, mechanical properties and electrical resistivity of rapidly solidified Pb-Sn-Cd and Pb-Bi-Sn-Cd alloys

A series of Pb-Sn-Cd alloys containing up to 60 wt % Bi were quenched from the melt to room temperature by melt spinning. The structure of rapidly solidified (melt spun), Pb-30 wt % Sn-10 wt % Cd, Pb-30 wt % Bi-20 wt % Sn-10 wt % Cd, and Pb-60 wt % Bi-10 wt % Sn-10 wt % Cd have been investigated by means of an X-ray diffraction technique. From X-ray analysis a crystalline metastable phase, designated (Pb-Bi) is detected. The formation of a metastable crystalline phase in the range of composition investigated causes a pronounced increase in the electrical resistivity. Desirable values of hardness and elastic constants are critically evaluated. It is also observed that the values of the Fermi energy are a few electron volts. Calculated values for the concentration of the conduction electrons, N, m_-3 of Pb -60 wt % Bi-10 wt % Sn-10 wt % Cd rapidly solidified is found to be 0.985×10₂₈ m_-3.     

Dynamic scaling and ultrasonic attenuation in 4He near the superfluid transition point

Attenuation of first sound has been measured in ⁴He under saturated vapor pressure near the lambda temperature T at frequencies /2 ranging from 10.2 to 271 MHz. The frequency dependence of the critical part of the attenuation is determined and the dynamic scaling hypothesis is examined. Above the lambda point, it is found that the critical attenuation is described by a scaling function (, ) = ^1+y F(), where = ₀^–x and = T/T – 1, with the results x = 1.02±0.05 and y = 0.33±0.03. The characteristic frequency of the order-parameter fluctuation with the wave number k equal to the inverse correlation length is then proportional to ^x , which is in an excellent agreement with the prediction of dynamic scaling. Below the lambda point, a characteristic relaxation time or times shorter than previously expected at lower frequencies appears to exist in the present frequency range.Based on a Ph.D dissertation submitted by K. Tozaki to the University of Tokyo (1977).     

Is there ferromagnetic to spin-glass transition in PdAuFe alloys?

Electrical resistivity studies on several (Pd_1–x Au _x )_99.93Fe_0.07 alloys between 25 mK and 1 K are reported. The experiments reveal interesting features of the impurity spin polarization with the addition of Au atoms to pure PdFe_0.07 alloy. Forx<0.28 the ternary alloys exhibit a familiarT ² dependence for belowT _c , indicative of complex magnetic behavior. For still higher Au concentrations, resistivity maxima occur in these alloys, reflective of short-range magnetic ordering. Arguments are presented to show that this is strongly suggestive of spin-glass-type freezing at lower temperatures, as is observed in many canonical metallic spin-glasses.     

Thermopower measurements on SiO x thin films

Thermopower and d.c. electrical conductivity measurements have been carried out between 125 and 625 K on SiO _x thin films, 130 nm thick, deposited on to Corning 7059 substratesin vacuo 1 mPa at 1.5 nm sec^–1. The thermopower, d.c. conductivity and their respective activation energies are fitted to a polynomial expression in 1/T. Below 400 K, the thermopower is negative, at 400 K the thermopower activation energy is approximately zero and the dominant current carriers are holes at the valence band edge, between 400 and 470 they are polaronic holes, between 470 and 590 K non-polaronic holes, and above 590 K electrons. Energy band diagrams are proposed for each temperature range studied.     

The preparation of high transition temperature superconducting Pb-Bi-Ge alloy filaments using the method of glass-coated melt spinning

The melt spinning of Pb-Bi-Ge alloys with Pyrex glass was investigated as a means of producing a superconducting long filament with highT _c. Continuous filaments with maximumT _c of more than 10 K of Pb_100-x-y Bi _x Ge _y (15x37 and 725) were obtained from the molten state at 1500 K with a winding speed of 0.95 m sec^–1. The Pb₄₉Bi₃₃Ge₁₈ filament, which was 34×10^–6 m diameter and a ductile material with a tensile strength of 20 MPa and elongation of 2.7%, exhibited superconductivity at the highestT _c of 14.3 K. These filaments were found to be polycrystalline with a grain size of more than 5000×10^–10 m and had a mixed structure of germanium (diamond) (h c p) and bismuth phases. The germanium element distributed homogeneously in the filament.