Upper Critical Field Hc2 on c Axis of Ag/Bi-2223 Polycrystal Tape

The upper critical field H _c2, based on Ginzburg–Landau theory at medial magnetic fields, can be calculated from the relationship of the magnetization intensity M(H) versus magnetic field H if M is linear with ln₀ H. For Ag/Bi-2223 tapes, the measured M(H) was found to be linear with ln₀ H. In this case, the values of H _c2(T) may in principle be determined. To do this, we will meet another problem in that the obliquity of crystal planes is not equal for different grains in tapes, and values of grain-oblique angle will appear in the calculated H _c2. Obviously, for Ag/Bi-2223 tapes is an uncertain parameter and hard to determine. To avoid the effects of , we only study the H _c2 in the c axis direction and the projections of H onto the c axis is taken as the actual applied fields. Thus, the effects of grain-oblique angle may be counteracted when measuring critical current density J, if the external magnetic fields are applied to the tape along both the parallel to and perpendicular to the c axes directions (on the narrow surfaces of the tape). On medial fields (H = 0 – 3 T), the upper critical fields H _c2(T) on c axis for the Ag/Bi-2223 tape are obtained and fitted as ₀ H _c2(T) = 830 e ^–0.07T . The average slope d[₀ H _c2(T)]/dT – 8T/K is found to be as large as that of Bi-2212. On extrapolating the relation to T = 0 K, the value of ₀ H _c2(0) 800T. The coherence length _ab is determined from H _c2(c), and _ab (0) = 0.63 nm at T = 0 K.     

Absorption Spectrum of ZnO Precipitates in ZnSe

The absorption spectrum of ZnO precipitates in ZnSe saturated with oxygen is studied in the spectral range 500–2000 cm^–1 and is shown to correlate with the transmission spectrum of single-crystal ZnO. Saturation of ZnSe with oxygen in the course of growth leads to ZnO precipitation during cooling. The precipitates give rise to narrow absorption bands in the range 5.8–7.1 m, which correlate with the components of the multiphonon absorption spectrum of ZnO, formed by combinations of LO and TO phonons. The 2LO mode defines the long-wavelength transmission edge of ZnO. In addition, the spectrum shows strong absorptions due to the LO + TO(10.2 m) and 2TO (11.3 and 12.7 m) modes. The possible role of SeO₂ is discussed. It is suggested that ZnO with a high carrier concentration may act as a gray filter in the spectral range 2–9 m.     

1 : 2 Long-range ordering and defect mechanism of WO3-doped perovskite Ba(Mg1/3Ta2/3)O3

The nature of the B-site cation ordering and the associated defect process necessary to stabilize the ordered domains were investigated using the WO₃-doped BaMg_1/3Ta_2/3O₃ BMT system as a typical example of BaB_1/3B_2/3O₃-type complex perovskites. It was shown that only the 1 : 2 long-range ordering of the B-site cation existed in both undoped and WO₃-doped BMT perovskites. The atomic defect mechanism associated with the stoichiometric 1 : 2 long-range ordering was systematically investigated. It is concluded that the substitution of W⁶⁺ for Ta⁵⁺ in the WO₃-doped BMT enhances the degree of the 1 : 2 long-range ordering and produces the positively charged W _Ta sites with a concomitant generation of tantalum vacancies V_Ta and mobile oxygen vacancies V _O for the ionic charge compensation.     

Equation of State and Thermodynamic Properties of Pure D2O and D2O + H2O Mixtures in and Beyond the Critical Region

A parametric crossover model is adapted to represent the thermodynamic properties of pure D₂O in the extended critical region. The crossover equation of state for D₂O incorporates scaling laws asymptotically close to the critical point and is transformed into a regular classical expansion far from the critical point. An isomorphic generalization of the law of corresponding states is applied to the prediction of thermodynamic properties and the phase behavior of D₂O + H₂O mixtures over a wide region around the locus of vapor-liquid critical points. A comparison is made with experimental data for pure D₂O and for the D₂O + H₂O mixture. The equation of state yields a good representation of thermodynamic property data in the range of temperatures 0.8T _c(x)T1.5T _c(x) and densities 0.35_c(x)1.65_c(x).     

Magnetic field dependence of the density of states of YBa2Cu3O6.95: Implications for the vortex structure

The total specific heat of YBa₂Cu₃O_6.95 single crystals includes contributions from phonons and spin-1/2 particles, as well as electronic contributions. The electronic specific heat is described by a quadratic term T² in zero field and a linear term [(0)+(H)]T which is increased when a magnetic field H is applied perpendicular to the CuO₂ planes. In agreement with d-wave superconductivity, we find that _n/T_c and (H)_n(H/H_c2)^1/2, where _n is the coefficient of the normal-state linear term. The H^1/2 dependence of the density of states at the Fermi level was predicted by G. Volovik for lines of nodes in the gap: the quasiparticles which contribute to this density of states are close to the nodes in momentum space and are located outside the vortex core.     

Energy Scales in the Local Magnetic Excitation Spectrum of YBa2Cu3O6+y

The wave-vector integrated dynamical spin susceptibility _2D() of YBa ₂ Cu ₃ O _6+y cuprates is considered. _2D is calculated in the superconducting state from a renormalized mean-field theory of the t–t–J-model, based on the slave-boson formulation. Besides the well-known 41 meV resonance a second, much broader peak ('hump') appears in Im _2D. It is caused by particle-hole excitations across the maximum gap ⁰ . In contrast to the resonance, which moves to lower energies when the hole filling is reduced from optimal doping, the position of this 'hump' at 2 ⁰ stays almost unchanged. The results are in reasonable agreement with inelastic neutronscattering experiments.     

Plastic deformation resistance of an indium-lead alloy with strain rates of 10−3–103 sec−1

Nonstandard A vs , N vs , and log vs diagrams were obtained for an indiumlead alloy using a common method together with standard vs diagrams. The strength, deformation, and energy characteristics and their variation coefficient were determined in the _pl.=10^–3–10³ sec^–1 plastic strain rate range. The influence of an increase in _pl on the plastic deformation resistance of the indium-lead alloy is revealed in a significant (up to 100%) increase in the strength and energy characteristics.Translated from Problemy Prochnosti, No. 3, pp. 53–57, March, 1990.     

Influence of Charge Doping on Thermal Diffusivity of Double Perovskite Sr2FeMoO6 Studied by Mirage Effect

Effects of charge doping on thermal diffusivity have been investigated in double perovskite ferromagnetic Sr_2–x La _x FeMoO₆ (0 x 0.4) by means of the mirage effect at 300 K ( the critical temperature T _c 420 K). Substitution of the La³⁺ ions for the Sr²⁺ ions significantly increases the value of the thermal diffusivity from 0.39 cm² · s^–1 at x = 0 to 0.54 cm² · s^–1 at x = 0.4. The increased thermal diffusivity is ascribed to the extra itinerant electrons on the Mo4d band.     

Synthesis and dielectric properties of pyrochlore solid solutions in the Bi2O3-ZnO-Nb2O5-TiO2 system

Phase studies of solid solutions based on (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ revealed extended regions of pyrochlore formation in the Bi₂O₃-ZnO-TiO₂-Nb₂O₅ system. At room temperature and 1 MHz (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ has a high permittivity ( = 200), low dielectric loss (tan<1·10^–4) and a temperature coefficient of the permittivity, , = –1300ppm/K. Pyrochlore solid solutions based on (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ can be formed with (Bi_2–xZn_x)(Ti_{2– x} Nb_x)O₇ (0.35x1.0) and with (Bi_1.5 Zn_0.5–y/3Ti_1.5+yNb_0.5–2y/3) O₇ (–1.5y0.75). Investigations of the dielectric characteristics showed that the high temperature dependence of the permittivity of (Bi_1.5 Zn_0.5)(Ti_1.5Nb_0.5)O₇ can be significantly modified by changing the composition of the pyrochlore within these regions of solid solubility. Below room temperature several of these compositions also exhibit a diffuse frequency dependent maximum in their permittivity characteristic of a transition to a relaxor type ferroelectric state. A third region of high permittivity pyrochlores with (Bi_1.5+2zZn_0.25–z Ti_2.25–z)O₇ (0.0z<0.15) was also identified in the Bi₂O₃-ZnO-TiO₂ sub system.     

Switching and Hysteresis on the I-V Curves of Submicron BSCCO (2212) Bridges

No Heading In thin BSCCO (2212) whisker-based superconducting bridges with width and length 1 m we observe random telegraph noise at discrete values of current. We show that the noise is associated with spontaneous processes of addition and removal of discrete vortex trains and reflects the regular structure of steps on the I–V curves. The average lifetime of the trains falls down with increasing temperature T in a complex way: intervals of steep drop ( an order of magnitude per Kelvin) are separated with a plateau of (T) with 10^–2 s. The 70 GHz irradiation with 100 W power results in the growth of the average switching frequency by 5 orders of magnitude; thus the HTSC bridges could be efficient detectors of microwave radiation. We discuss the peculiar features of (T).PACS Numbers: 74.25.Fy, 74.40.+k, 74.60.Ge, 74.72.Hs     

Infrared absorption ofβ-SiC particles prepared by chemical vapour deposition

Infrared absorption characteristics of-SiC particles prepared by chemical vapour deposition were studied. These particles were either solid or had a silicon core and/or were hollow. The solid particles exhibited a single absorption peak between the transverse optical frequency (_TO = 794 cm^–1) and the longitudinal optical frequency (_LO = 976 cm^–1) of-SiC. This absorption peak shifted to a lower frequency with increasing lattice parameter of-SiC and increasing free silicon content. The particles containing a silicon core and/or were hollow exhibited double absorption peaks close to _TO and _LO. The peak at the LO side shifted to a lower frequency and that at the TO side to a higher frequency with decreasing silicon core size and increasing hollow size. Using the calculations based on the effective medium theory assuming surface phonon mode, the relationship between the infrared absorption characteristics and microstructures of the-SiC particles are explained.     

Interfacial spring model for ultrasonic interactions with imperfect interfaces: Theory of oblique incidence and application to diffusion-bonded butt joints

The quasi-static distributed spring model is used to derive the ultrasonic reflectivity of an imperfectly-bonded interface as a function of frequency and angle of incidence. The results are then incorporated in a model for the corner reflection from a diffusion-bonded joint between two abutting plates, the corner being defined by the bond plane and the common lower surface plane of the plates. An immersion-inspection geometry is assumed, and seven categories of corner reflections are identified and examined in detail. These fall into two classes: those having parallel incident and exiting rays in water (=), and those having nonparallel water rays ( ). The = categories are suitable for single probe (pulse-echo) inspections of the joint. Based on the amplitude of the outgoing corner-reflected signal, two = geometries appear promising. These employ, respectively, a corner reflection involving only longitudinal waves with the interface illuminated at near-grazing incidence (LLL), and a corner reflection involving only transverse waves with the interface illuminated at near 45° incidence (TTT). In addition, two practical geometries are indicated; these both involve mode conversion upon reflection from the interface, with the incident or outgoing longitudinal wave traveling nearly parallel to the interface. Model predictions for LLL and TTT reflections are compared to measurements on diffusion-bonded Inconel specimens, and techniques for applying the model results to more complicated bond geometries are discussed.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Shear viscosity of the B phase of superfluid 3He. II. s-p-d-wave approximation

The shear viscosity (T) of superfluid ³He-B is studied throughout the temperature region 0t1 (t=T/T _c). The Boltzmann equation for Bogoliubov-Valatin quasiparticles is solved by a variational method. In the calculation of the collision integral, the scattering amplitude is estimated in the s-p-d-wave approximation by taking into account the spin-dependent part as well as the spin-independent part. The reduced shear viscosity % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-qqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xHapdbiqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaacaaeaacq% aH3oaAaiaawoWaaiabg2da9iabeE7aOHqaciaa-HcaieaacaGFubGa% a8xkaGGaciab99caViabeE7aOjaa-HcacaGFubWaaSbaaKqaGgaaca% WFJbaaleqaaOGaa8xkaaaa!440E!\[\widetilde\eta = \eta (T)/\eta (T_c )\] in this approximation is smaller than those in the s-wave and s-p-wave approximations at all temperatures. The numerical result for \~ in the s-p-d- wave approximation is in good agreement with the recent experimental data of Parpia et al. and of Alvesalo et al. in the temperature range 0.5.t1.0.Supported in part by the Nishina Memorial Foundation and in part by the NSF under Grant No. DMR-76-24011.     

Low endurance fatigue in metals and polymers

The fatigue behaviour of commercially pure aluminium and of nylon under sequentially varying strain amplitudes is compared with a damage law of the type suggested by Miner. Aluminium obeys such a law for both cyclic and uniaxial prestrains but the behaviour of nylon is significantly affected by microcracking, which produces a marked effect of loading sequence.Appendix N Number of strain cycles at a given time - N _f Value of N at failure - True tensile stress - True stress range for a strain cycled specimen - _h Value of at half the life of the specimen - True tensile strain - Total true strain range - _p True plastic strain range (= the breadth of the hysteresis loop at = 0) - _d True diametral strain range - E Young's modulus - Linear strain hardening rate when tested at a particular value of _p - D Damage due to cycling - D _p Damage due to prestrain - _p Prestrain. C, K, K₁, , are constants     

Structure and Magnetism of the Composite Crystal Ca0.824CuO2

We have studied the magnetic state from a viewpoint of crystallographic features of the 1-D chain compound Ca_0.824CuO₂. A possible spin-hole arrangement in the magnetically coexisting state was determined by analyzing the local structural distortion in the CuO₂ chain by means of a modulated-crystal-structure analysis. The essential periodic sequence expected is (: up- and down-spin, : hole), which can be regarded as a kind of spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain.     

Localized single-particle excitations and the density of states for superconducting composites

The problem of localized single-particle excitations and the density of states (DOS) for an inhomogeneous system consisting of a spherical superconductor (with radius a and order parameter ₁) embedded in another superconductor (order parameter ₂) of infinite size is considered. With the assumption of constant values of ₁ and ₂, the Bogoliubov equations are solved for general values of l (the orbital angular momentum quantum number). For a fixed value of ₁/₂ and different values of ₂/E _F, the dependence of the excitation energy (l=0)/₂ on the particle sizek _F a is shown (k _F is the Fermi wave vector andE _F is the Fermi energy). Fork _F a=300, 450, and 800 and a fixed value of ₂/E _F, the variations in the DOS by changing ₁/₂ are also shown.     

Accuracy of temperature measurements in determining the thermal conductivity of substances by stationary methods in the range of moderate temperatures

An empirical comparison is made of the accuracy of platinum-rhodium-platinum and Chromel-Alumel thermocouples in determining the thermal conductivity of substances.Notation T, t temperature - temperature difference - y thermocouple readings - A_i parameters of approximating equation - sensitivity of thermocouple - sensitivity found from the generalized function - _st standard values of sensitivity - S₀ standard deviation of sensitivity for a given series - maximum deviation of from in different series - I, II indices indicating that the values pertain to platinum-rhodium —platinum and Chromel —Alumel thermocouples, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 306–310, August, 1980.     

Fatigue properties of pure metals

The report considers the stress fatigue limit _D, the fatigue to tensile strength ratio _D/R_m, and the deformation fatigue limit _D of pure metals. For FCC and some HCP metals there exists a linear correlation between fatigue limit and tensile strength. The fatigue limit and the fatigue ratio _D/R_m depend upon the homologous temperature. The fatigue ratios of BCC metals are higher than the fatigue ratios of other metals at room temperature as is also true for metals with nearly the same homologous temperature. The deformation fatigue limit decreases rapidly when T_h - 0.5 and T_h 1. When T_h = 1 then _D = 0, _D = 0 and _D/R_m = 0. The deformation fatigue limits of metals belonging to the same subgroup of the periodic element system and having, similar homologous temperatures at room temperature are very similar.

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Zusammenfassung Der Artikel behandelt die Dauerfestigkeit _D des Ermuedungskoeffizienten _D/R_m und die Deformation _D, die der Dauerfestigkeit entspricht. Fuer kubisch flachzentrierte Metalle und einige hexagonal Metalle existiert eine lineare Korrelation zwischen Dauerfestigkeit _D and Zugfestigkeit R_m. Die Dauerfestigkeit _D und der Ermuedungskoeffizient _D/R_m koennen als Funktion der homologischen Temperatur betrachtet werden. Der Ermuedungskoeffizient der kubisch raumzentrierten Metalle ist groesser als der der anderen in Raumtemperatur. Dieses stimmt auch fuer Metalle mit aehnlichen hornologischen Temperaturen. Die Deformation _D, die der Dauerfestigkeit entspricht, faellt schnell ab, wenn T_h > 0.5 und T_h 1, Wenn T_h = 1, darn ist _D = 0, _D = 0 und _D/R_m = 0. Die Metalle, die zu derselben Gruppe des periodischen Systems der Elemente gehoeren and aehnliche homologische Temperaturen (in Raumtemperatur) besitzen, haben sehr aehnliche Werte der Deformation _D.

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Résumé L'article parle de la contrainte de la limite de fatigue _D le facteur de fatigue _D/R_m et la déformation _D correspondante à la limite de fatigue des métaux pures. Pour les métaux du système cubique aux faces centrées (c. f. c.) et quelques uns du système hexagonale (hex. c.) il existe une correlation linéare entre la limite de fatigue _D et de la résistance a la fraction R_m. La limite de fatigue _D et le facteur de fatigue _D/R_m dependent de la température homologue. Les facteurs de la fatigue des métaux du système cubique centre (c.c.) sort plus grands que ceux des autres métaux dans la température de chambre, aussi por des métaux qui ont presque la même température homologue. La déformation correspondante à la limite de fatigue tombe rapidement quand T_h > 0.5 et T_h 1. Quand T_h = 1, alors _D = 0, _D = 0 et _D/R_m = 0. Cettes déformations _D pour les métaux du même groupe du système périodique des éléments sont proches si les températures homologues dans la température de chambre sont analogues.

     

The thermal conductivity and Lorenz function of the tin-lead alloy system Sn x Pb1 − x (x = 0.85, 0.7 0.5 0.3)

The thermal conductivity and electrical resistivity of the tin-lead alloy system Sn _x Pb_{1 – x} (x = 0.85, 0.7 0.5 0.3) were measured in the temperature range 7–300 K. The thermal conductivity was analyzed at temperature T 20K, assuming 1//T+Tⁿ, where , , and n are constants. The analysis shows that n < 2, and not n 2, which would be expected for a normal pure metal. The electrical resistivities could be represented by a T ⁵ relation for temperatures up to about 60 K. The characteristic temperature _R appears to decrease with increasing weight percent of lead. The total Lorenz functions were high, indicating the presence of phonon conductivity. The phonon conductivity _g appears to vary with T, and can be represented by _g=a/Tⁿ (a > 0) and n2.Work supported by the Universiti Sains Malaysia.