Viscous flow behaviour of NixZr100−x metallic glasses from Ni30Zr70 to Ni64Zr36

The compositional dependence of viscous flow in the Ni _x Zr_100–x amorphous system was investigated under non-isothermal conditions at a heating rate of 10 K min^–1in the compositional range fromx=30 tox=64 at % with the aid of a Hereaus TMA 500 dilatometer. The crystallization behaviour of the same glassy alloys under the same non-isothermal conditions was studied with a Perkin-Elmer DSC 7 differential scanning calorimeter. The characteristic crystallization and viscous flow parameters (the onset temperature,T _x, of crystallization; the temperature,T _m, of maximum heat evolution of the first crystallization step; the enthalpy, H _x, of crystallization; the activation energy,Q _x, of crystallization; the glass transition temperature,T _g; the viscosity values (T _g) and _min; and the activation energy for viscous flowQ (T>T _g), were shown to be dependent on composition. This dependence was examined on the basis of the equilibrium phase diagram of the Ni-Zr-system, and it is shown that glassy alloys possessing eutectic compositions manifest the greatest thermal stability because of the long-range atomic diffusion needed for crystallization to occur. Glassy alloys with nearly peritectoid compositions show low thermal stability, as no long-range diffusion is needed for the formation of the stable crystallization end-products NiZr₂ and NiZr. In all cases, the crystallization process is governed by viscosity flow of these glassy alloys.     

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.     

A review of the size of the energy gap in superconducting oxides

An attempt has been made to summarize a large body of data dealing with measurements of the energy gap in superconducting oxides like La_2–x Sr _x CuO_4–y , YBa₂Cu₃O_7–y , and related compounds. A plot of available data of the energy gap 2 as a function of the superconducting transition temperatureT _c revealed a large dispersion of some data from 2/k _B T _c =3.53 for the weak coupling BCS prediction. Nevertheless, we could conclude that the size of the energy gap in these exotic materials is within the weak coupling BCS prediction, in view of some controversial issues that could be responsible for the dispersion, such as the gap anisotropy as well as identification of the energy gap.     

Thermal properties of new molybdenum oxyfluoride glasses

New oxyfluoride glasses were prepared in the form MoO₃-BaF₂-xRF where RF is alkali fluoride (LiF, NaF and mixed NaF–LiF) with x = 5, 10, 15, 20, 25, 30 and 35 mol%. The densities of the studied glasses were measured and the molar volumes were calculated. Thermal properties like glass transition temperature T _g, the onset of crystallization temperature T _x , crystallization temperature T _c and melting temperature T _m were determined by using the differential scanning calorimetry (DSC) technique and from which the glass stability S and the glass forming tendency K _g were calculated. Values of thermal expansion coefficient and specific heat C _p of the present glasses were also measured. All the above properties are correlated with composition alkali fluoride RF content and structure of the glass.     

Critical light scattering in4He near the gas-liquid critical point

Scattered intensities of light were measured near the gas-liquid critical point of ⁴ He at scattering angles of 30, 60, and 90° as functions of the reduced temperature =|T–T _c |/T _c along the critical isochore (T>T _c ) and the coexistence curve (T>T _c ). The temperature range was 3×10 ^–5 <<1.5×10 ^–2 . Critical exponents and coefficients describing divergence of the generalized susceptibility and the correlation length are obtained as (T>T _c )=1.31±0.02, v(T>T _c )=0.66±0.02, ₀ (T>T _c )=4.2±0.6 Å, (T>T _c )=1.32±0.02, v(T>T _c )=0.68±0.02, _± (T>T _c )=2.6±0.7 Å, =0.06±0.06(T>T _c ), 0.05±0.05(T>T _c ), and ₀(T>T _c )/x_± (T>T _c )=3.6±0.4. It is pointed out that the quantal nature of ⁴ He has remarkable influence on the critical behavior of ⁴ He in the above-mentioned temperature region.     

d-Hole localization and the suppression of superconductivity in YBa2(Cu1-xZnx)3O7?y

The temperature and Zn concentration dependence of the electrical resistivity, specific heat, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectra of YBa₂(Cu_1–x Zn _x )₃O_7–y withy0.1 has been measured forx0.16. In addition, the temperature and field dependence of the magnetization has been measured for 2<T<300K and 0<H<9.0T, along with the temperature and quasihydrostatic pressure dependence of the electrical resistivity for selected samples for 0<P<13 GPa. The substitution of Zn for Cu in YBa₂Cu₃O_7–y causes a rapid and nearly linear depression of the superconducting transition temperature,T _c , withT _c going to 0 K forx 0.10. YBa₂(Cu_1–x Zn _x )₃O_7–y retains the YBa₂Cu₃O_7-y orthorhombic structure forx0.16 for both the superconducting and nonsuperconducting samples. Initially, the unit cell volume increases nearly linearly with Zn content; however, an abrupt change occurs in the vicinityx=0.8–0.10. Forx<0.10, the temperature dependence of the electrical resistivity,(T), is metallic-like (d/dT>0) and increases gradually with increasing Zn content. However, forx 0.10,(T) becomes semiconductor-like, with a very rapid increase of the resistivity with increasingx. The electrical resistivity, magnetic susceptibility, EPR spectra, and specific heat all indicate that thed-holes associated with the Cu ions become localized in the nonsuperconducting phase,x>-0.10.     

Ga as an additive in the As2Te3 glass

Results of measurements of the mean atomic volume (V), the glass transition temperature (T _g), the activation energy for glass transition (E _t) and the d. c. electrical conductivity () are reported and discussed for ten glass compositions of the Ga–As–Te system. The glasses studied can be represented as Ga _x (As_0.4Te_0.6)_100–x glasses, with the additive Ga ranging from 0 to 12 atomic percent (at.%) in the parent As₂Te₃glass. In the Ga _x (As_0.4Te_0.6)_100–x glasses, changes in slope are observed in the V, T _g, E _t, and other electronic properties, at the composition with a Ga content of 2 at.%. The results are compared with those obtained on introduction of Ag and Cu to the As₂Te₃and the [0.5As₂Te₃–0.5As₂Se₃] glasses. Analysis of the data suggest formation of GaAs, Ga₂Te₃and excess Te structural units (s.u.) in lieu of some of the original As₂Te₃s.u., for addition of Ga up to 2 at.% to the parent As₂Te₃glass; for higher Ga contents, formation of GaAs, GaTe and excess Te s.u. are indicated.     

Preparation and study of Ca1 − xMgx(PO3)2 glassy and crystalline phases

The structure of Ca_{1 – x} Mg _x (PO₃)₂ crystalline and glassy samples was investigated in the whole concentration region of x = 0–1.0. From X-ray diffraction data it was found that, in the crystalline samples, solid solutions are formed for x < 0.3 on the calcium-side of the system, with the structure of -Ca(PO₃)₂, and for x > 0.6 on its magnesium-side, with the structure of Mg₂P₄O₁₂. Similar results were obtained from the study of their infrared and Raman spectra. In the glassy state, homogeneous glasses were formed within the whole concentration region. The values of their transformation temperatures, T _g, and crystallization temperature, T _c, change slightly with the composition and lie within the region of T _g = 529–544 °C and T _c = 631–677 °C.     

Extraordinary behaviour of the Y1?xPrxBa2Cu3O7?δ system

Investigations of Y_1–x M _x Ba₂Cu₃O_7– (M=Ce, Th)c-axis oriented thin film specimens show that the rate of depression ofT _c withx is larger for M=Th, than for M=Ce and Pr, and suggest that Ce, like Th, is tetravalent in this compound. Hall effect measurements on Y_1–x Pr _x Ba₂Cu₃O_7– single crystals reveal aT ² dependence of the cotangent of the Hall angle in the normal state and a negative Hall anomaly belowT _c in the superconducting state, in agreement with recent reports. Our research shows that the depth, , of the negative Hall signal scales withT/T _c and that the maximum value of decreases linearly withx and vanishes atx0.24. Magnetoresistance measurements on Y_1–x Pr _x Ba₂Cu₃O_7– single crystals indicate that the irreversibility lineH(T ^*) obeys a universal scaling relation characterized by anm=3/2 power law nearT _c, with a crossover to a more rapid temperature dependence of belowT/T _c 0.6, similar to that observed for polycrystalline specimens.     

High-T c superconducting Bi(Al)-Ca-Sr-Cu-O glass-ceramic fibres drawn from glass preforms

Bi(Al)-Ca-Sr Cu-O glass-ceramic fibres over 100 cm in length were successfully drawn from a glass preform above the crystallization temperature,T _x. The diameters of the uniformly drawn fibres with circular cross-section could be controlled in the range from 25–200 m and the drawing speed was as high as 200 cm min^–1. In this work Al₂O₃ was used to modify the properties of the glass. It increased the glass transition and crystallization temperatures but did not significantly increase the glass working range. Shrinkage and increase of density during heat treatment of the glass fibres were observed. The annealed (825°C/12 h in air) Bi₄Al_0.1Ca₃Sr₃Cu₄O_y glass-ceramic fibre showed aT _c(onset) of 82 K and aT _c(zero) of 71 K.     

Phase Relations in the SrO–Bi2O3–Fe2O3 System

The phase relations in the composition region SrFeO_{3 –} –Fe₂O₃–BiFeO₃ are studied in air by x-ray diffraction and electron microscopy. The 1000°C phase compatibility diagram is constructed. Sr_{1 – x} Bi _x FeO_{3 –} solid solutions are prepared in the range 0 < x 0.8. Their lattice parameter is found to vary nonlinearly with x. Two new phases were identified: (Sr,Bi)₃Fe₄O _y (tetragonal lattice, a= 3.907(2) Å, c= 27.30(2) Å) and Sr_0.6Bi_0.4FeO_{3 –} (tetragonal lattice,a = 5.555(2) Å, c= 11.848(5) Å).     

Non fermi liquid ground states in strongly correlated f-electron materials

Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for three f-electron systems: M_1–xU_xPd₃ (M = Sc, Y), U_1–xTh_xPd₂Al₃, and UCu_5–xPd_x. The emerging systematics of NFL behavior in f-electron systems, based on the present sample of nearly ten f-electron systems, is updated. Many of the f-electron systems exhibit the following temperature dependences of the electrical resistivity p, specific heat C, and magnetic susceptibility for T T₀, where T_o is a characteristic temperature: P(T) 1 –aT/T ₀, where a < 0 or > 0, C(T)/T (-1/T _o) In (T/bT ₀), and (T) 1 –c(T/T_o)^1/2. In several of the f-electron systems, the characteristic temperature T_o can be identified with the Kondo temperature T_k.     

Low-temperature specific heat of YBa2Cu3O7, YBa2Cu3O6, Y2BaCuO5, YBa3Cu2O7, BaCuO2, and CuO

We have measured the low-temperature specific heat (1.3T20 K) and the dc magnetic susceptibility (100T250 K) of eight samples of the high-T _c superconductor Y _x Ba_3–x Cu₃O_7– (x=0.9, 1.0, 1.1) and of two samples of nonsuperconducting YBa₂Cu₃O₆₊. We have also performed specific heat measurements on the possible impurity phases: YBa₃Cu₂O₇, Y₂BaCuO₅, CuO, and BaCuO_2+x . The superconducting samples all have a nonzero, sample-dependent linear term * and an upturn inC/T at very low temperature. We show that this anomalous behavior is at least partly due to the presence of a small amount (1%) of BaCuO_2+x impurity phase in the measured samples. This is evidenced by the correlation between * and the Curie component of the susceptibility, which is proportional to the amount of paramagnetic impurities.     

Thermal properties of multicomponent tellurite glass

Quaternary tellurite glass systems of the form 80TeO₂–5TiO₂–(15 − x)WO₃ − xA_nO_m where A_nO_m is Nb₂O₅, Nd₂O₃, and Er₂O₃, x = 0.01, 1, 3, and 5 mol% for Nb₂O₅ and x = 0.01, 0.1, 1, 3, 5, and 7 mol% for Nd₂O₃ and Er₂O₃, have been prepared by the melt quenching. Density and molar volumes have been measured and calculated for every glass system. The thermal behavior of the glass series was studied by using the differential thermal analysis DSC. Glass transition temperature T _g, crystallization temperature T _c, and the onset of crystallization temperature T _x were determined. The glass stability against crystallization S (≈100 °C) and glass-forming tendency K _g (≈0.3) have been calculated. Specific heat capacity C _p (≥1.4 J/g °C) was measured from room temperature and above the T _g for every composition in each glass series. Quantitative analysis of the above thermal properties of these new tellurite glass with the structure parameters like average cross-link density (≥2.4), number of bonds per unit volume n _b (≥8 × 10²⁸ cm⁻³), and the average stretching force constant (F) have been studied for every glass composition.     

Evolution of transient thermal processes in layer counterflow apparatuses and heat exchangers

Results are given of an analytic investigation of transient processes inside counterflow apparatuses and heat exchangers with temperature disturbance in one of the heat carriers at the entry to the apparatus.Notation =(t–t₀)/(T₀–t₀),=(T–t₀)/(T₀ s-t₀) relative temperatures - t, T temperatures of material and gas respectively - t₀, T₀ same for the initial state - Z=[ _Vm₁/c(1–w/w_g)] [–(y₀–y)/w_g] dimensionless time - m₁=1/(1+Bi/) solidity coefficient - B₁=( _FR/) Biot number - _{F V} heat-exchange coefficients referred to 1 m² surface and 1 m³ layer - R depth of heat penetration in a portion - portion heat conductivity coefficient - shape coefficient (=0 for a plate,=1 for a cylinder,=2 for a sphere) - c, C_g heat capacities of material and gas respectively - , _g volumetric masses - w, W_g flow velocities of material and gas - y distance from the point of entry to the heating heat carrier - y₀ heat-exchanger length - Y= _Vm₁y/W_gC_{g g} dimensionless coordinate - m=cw/C_g– _gW_g water equivalent ratio Deceased.Translated from Inzhenerno-Fizicheskii Zhurnal, vol. 20, No. 5, pp. 832–840, May, 1971.     

The influence of composition on the formation and stability of Ni-Si-B metallic glasses

The influence of composition on the formation and stability of Ni-based glassy alloys containing Si and B has been investigated systematically. Depending on the SiB ratio certain compositions, with total metalloid contents in the range 17 to 49 at% (a wider range than has hitherto been reported for metal-metalloid glasses), have been vitrified by melt-spinning to an average thickness of 17 m. For metalloid concentrations greater than 36 to 40 at% the amorphous phase is brittle in the as-quenched state. The highest crystallization temperatures, T _x, occur at 32 to 38 at% metalloid, the actual value of T _x again depending on the SiB ratio. It is shown that, over a wide composition range, the glass-forming boundary corresponds closely with a value for the reduced crystallization temperature isometric of 0.52. This value corresponds to a critical cooling rate for glass formation of about 10⁶ K sec^–1, predicted from kinetic theories and assuming that T _x is a good estimate of the glass transition temperature, T _g. This agrees quite closely with the cooling rate for approximately 17 m thick tape predicted from thermal studies of the melt-spinning process. Hence, T _x/T _liq usefully describes the glass-forming ability (GFA) for much of the composition range studied, although preliminary results suggest that near the centre of the glass-forming range the GFA may be over-estimated. Substitution of Si by other metalloid elements from Groups IIIb–Vb in Ni₇₈Si₁₀B₁₂ glassy alloy generally decreases the thermal-stability.     

Crystallization kinetics of bulk amorphous (Se65Te35)100−x Sb x

Kinetic studies of crystallization in (Se₆₅Te₃₅)_100–x Sb _x with 0x10 glasses, using the differential scanning calorimetry technique, were performed. Crystallization enthalpy data, H _c, were collected as a function of composition. The crystallization data were examined in terms of recent analyses developed for non-isothermal crystallization studies, to arrive at E _c. The results indicate bulk nucleation and crystallization with two- and three-dimensional growth, respectively, for the (Se₆₅Te₃₅)₉₈Sb₂ and (Se₆₅Te₃₅)₉₂Sb₈ glass composition.     

Density,differential thermal analysis and direct-current conductivity of Sb10S90 −x Ge x chalcogenide glasses

The glass-transition temperature,T _g, and the crystallization temperature,T _c for glassy Sb₁₀S_{90 –x} Ge _x samples were increased by increasing the Ge content. This was attributed to the closeness of the network by bridging Sb and/or S atoms with additional Ge atoms to form harder Ge&#x2013;Sb and/or Ge&#x2013;S bonds. The direct current (d.c.) electrical conductivity for the system Sb₁₀S_{90 –x} Ge _x shows semiconducting behaviour with increasing temperature. At low temperatures, the conductivity was attributed to a hopping conduction mechanism, while at high temperatures it was due to regular band-type conduction. The activation energy, E and the conductivity, ₀ were increased at low Ge contents. This may be related to the entrance of Ge atoms into the S&#x2013;S chains. On the other hand, the increase of the Ge content above 20 at % lead to a conversion of the behaviour of the E and ₀ from the insulating character of S to the semiconducting character of Ge.