Effect of microstructure and fusion temperature on the electrical and optical properties of vanadate glasses

The electrical and optical properties of binary semiconducting oxide glasses containing 45 mol % V₂O₅ and 55 mol % GeO₂ fused and equilibrated at various temperatures (T ) in air were measured.T was varied over the range from 1000 to 1350° C. Their electrical and optical properties are shown to be sensitive to microstructure and melt temperature. We suggest that the change inT caused progressive microstructure changes of these glasses, which dramatically affected the electronic conductivity and the activation enthalpy for conduction.     

Disappearance of Bose-Glass Behavior in Transport Properties of YBa2Cu3O y Films with Columnar Defects

The glass transitions of the vortex system in Au-ion irradiated YBa₂Cu₃O _y films have been studied by the measurements of transport properties as a function of magnetic field B and angle of B to the direction of columnar defects. At =0°, we find an anomalous upturn behavior of the glass transition line B _g(T) at BB /3, where B is the matching field. In B>B /3, the dependence of glass transition temperature T _g reveals cusplike behavior with a peak at =0°, which is consistent with the Bose glass theory. In B<B /3, on the other hand, T _g is almost independent of , suggesting the system undergoes the vortex glass transition induced by the inherent point-like defects.     

Mössbauer study of the dynamical properties of some lead borate glasses near their transformation temperature

Calcium-lead-borate glasses containing iron were thoroughly studied by Mössbauer effect spectroscopy aiming to determine both their Debye temperature and their transformation temperature during heating. The obtained Mössbauer effect parameters at room temperature exhibit dispersion of iron ions in a low spin ferric state as modifying cations in a pure amorphous glass matrix. The electric field gradient due to the lattice was stabilized at moderate and high lead oxide content glasses. The high-temperature measurements were carried out between 300 and 750 K under vacuum. It can be concluded that the recoil-free fraction decreased and the mean square amplitude of the Mössbauer atom increased as the temperature was increased. From the Inf againstT curve, the Debye temperature of the solid glass can be calculated (_D = 373.8K). The experimentally determined transformation temperature from this study was found to be 665 K, which may be slightly less than the real value.     

An analysis of the high-temperature entropy of transition metals

The high-temperature entropy at constant pressure, obtained from heat capacity data, is analyzed for Mo, Nb, Pd, Rh, Ru, Sc, Ti, V, W, Y, and Zr. The vibrational contribution to the entropy defines an entropy Debye temperature, _S(T). Due to anharmonicity, _S(T) decreases with the temperature T, typically by 10–20% between room temperature and the melting point. An unusual temperature dependence of _S(T) may indicate inadequacies in the underlying data. On this ground, the C _p data recommended by Hultgren et al. (1973) for W and Ru seem doubtful. A comparison is made between _S and the elastic-limit Debye temperature _D for the metals with a cubic lattice structure. _S of Nb is found to be almost independent of T, a feature related to the fact that the elastic constant c ₄₄ increases with T.     

Small polaron transport in V2O5–NiO–TeO2 glasses

Semiconducting glasses of the V₂O₅–NiO–TeO₂ system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 300–450 K were measured. The d.c. conductivities at 395 K for the present glasses were determined to be 10^–7 to 10^–1 S m^–1, indicating that the conductivity increased with increasing V₂O₅ concentration. A glass of composition 67.5V₂O₅–2.5NiO–30TeO₂ (mol %) having a conductivity of 2.47×10^–2 S m^–1 at a temperature of 395 K was found to be the most conductive glass among the vanadium-tellurite glasses. From the conductivity–temperature relation, it was found that a small polaron hopping model was applicable at the temperature above _D/2 (_D: the Debye temperature); the electrical conduction at T>_D/2 was due to adiabatic small polaron hopping of electrons between vanadium ions. The polaron bandwidth ranged from 0.06 to 0.21 eV. The hopping carrier mobility varied from 1.1×10^–7 to 5.48×10^–5 cm² V^–1 s^–1 at 400 K. The carrier density is evaluated to be 1.85×10¹⁹–5.50×10¹⁹ cm^–3. The conductivity of the present glasses was primarily determined by hopping carrier mobility. In the low-temperature (below _D/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.     

3-D Simulations of Diffusivity Measurements in Liquids with an Applied Magnetic Field

The effect of convective contamination in self-diffusivity experiments of liquid metals is predicted via a three-dimensional (3-D) model that includes an applied magnetic field. A uniform heat flux is applied at the sidewall of the cylindrical ampoule, and heat losses are allowed at the top and bottom walls of the ampoule. A wide range of a uniform, steady, axial magnetic field (from moderate to very strong) is considered in the model. Since the thermal Peclet number, Pe, is very small for the parameters of interest, convective heat transfer is neglected. A large interaction parameter, N, suggests that the flow is inertialess. The temperature and flow problems are solved at steady state while the time-dependent concentration problem is determined for various mass Peclet numbers, P e. In all cases, the output D (i.e., with convective contamination) increases with an increase in the temperature non-uniformity T. The radial and azimuthal velocities are much smaller than the axial velocity in each case. A stronger magnetic field can tolerate a higher temperature non-uniformity T, but T is still less than 0.025 K with a 5 T magnetic field for convective contaminations to be less than 5 of the total mass flux.     

Effect of plastic deformation on the superconducting transition temperatures of tin,bismuth-thallium,and bismuth-lead specimens

The enhancement of the superconducting transition temperatureT _cof tin by 100%, of bismuth-thallium by 32%, and of bismuth-lead by 22% due to plastic deformation is reported. It is found that the transition to the superconducting state is sharp. The resistivity and the critical fieldH _c(0) are greatly affected. The electronic specific heat coefficient , the Debye temperature _D, the density of states at the Fermi surfaceN(0), and the coupling constant are computed for the undeformed and the deformed states. These parameters are also greatly affected by plastic deformation. The enhancement ofT _ccan be attributed to changes in _D and .     

Low-temperature specific heat of high-purity calcium

Low-temperature specific heat of high-purity calcium has been measured with an adiabatic calorimeter with a mechanical heat switch to avoid helium exchange gas errors, over the temperature range 1.1–4.2 K. The values obtained for the electronic coefficient of specific heat and the Debye temperature _D are =1.99±0.05 mJ/moleK ² and _D=250±4K.     

Coupling behavior of Cu-O2 layers in oxygen-deficient YBCO films and ultrathin YBCO films

We have measured the resistivity as a function of temperature in a magnetic field at various field angles for oxygen-deficient YBCO films and ultrathin YBCO films; is the angle between the crystalc axis and the direction of the magnetic field. The angular dependence of the critical field,H _c2, shows a cusplike behaviour at =90° for the oxygen-deficient 60 K YBCO films indicating that the Cu-O₂ layers are two-dimensional in nature. BothT _c versus in a constant field andH _c2 as a function of show a plateau at =90° for 83 K (zero resistance) ultrathin YBCO films with a thickness of 20 units of the YBCO cell; these results indicate that there is a coupling between the Cu-O₂ layers. The dimensionality of the Cu-O₂ layers in oxygen-deficient YBCO films and ultrathin YBCO films is discussed in terms of the anisotropic Ginzburg-Landau model and the Tinkham thin-film model.     

Low-temperature specific heat anomalies in the group V transition metals

Anomalies previously reported in the specific heat curve of normal-state niobium at 3 and 9.5 K prompted new measurements on single crystals of niobium, tantalum, and vanadium from their superconductingT _c 's up to 20 K. The upper anomaly was confirmed in Nb and found to occur at 10.3 K. At this temperature theC/T vs. T ² curve changed abruptly from a line with constants ₂ =7.67 mJ/K ² mole and ₂ =241 K to one with ₃ =9.16 mJ/K ² mole and ₃ =250 K. The NbT _c was 9.275 K. Anomalies similar to that occurring at 3 K in the niobium curve were discovered to exist in tantalum and vanadium as well, but at the higher temperatures of 7.19 and 7.47 K, respectively. The tantalum data yielded line constants of ₁ =5.42 mJ/K mole, ₁ =238 K, ₂ =4.36 mJ/K ² mole, and ₂ =228 K and aT _c of 4.475 K. For vanadium ₁ =397 K is higher than previous specific heat values of ₁ =382 K, and in agreement with that obtained from elastic constant measurements (399 K). The discontinuities in the slopes of the specific heat curves are analyzed in terms of anomalies in the electron and phonon spectra of the materials investigated.     

Electrical conductivity of sol-gel derived metal nanoparticles

Electrically conducting films of thickness 2 m have been prepared on ordinary glass slides by growing ultra-fine particles of iron and copper, respectively, from a suitable precursor sol. The diameters of metal particles can be varied from 3–13 nm by controlling the heat-treatment schedule of the sol coating. Resistivity measurements (d.c.) have been carried out over the temperature range 80–300 K. The resistivity values in the range 0.0001–0.0039 cm have been obtained depending on the particle diameter and the type of metal used. The effective Debye temperature _D for the different nanoparticle systems have been estimated by fitting the experimental data to the Ziman equation. _D is found to vary from 346–408 K for iron with the particle size in the range 3.4–9.5 nm. The values obtained for copper are 243–307 K with particle diameters covering a range of 5.9–12.6 nm.     

High-field specific heat of A-15 Mo0.4Tc0.6

The specific heat of A-15 Mo_0.4Tc_0.6 has been, measured in a 7-T magnetic field in order to suppress the superconducting transition. With normal state data now available from 7 to 25 K, an improved determination over previous work of and 2/kT _c was possible. Thus, more accurate values for (6.2±0.5mJ/g-atom K²) and 2/kT _c (5.3±0.5) have been determined. These parameters present a more believable picture of the strong coupling behavior of A-15 Mo_0.4Tc_0.6 than previously presented. In addition, the low-temperature specific heat data were extended to 1.4 K from the previous work's low of 4 K. These new data enable a determination of _D at T = 0 (349±5 K) and _D at 7 K (306±5 K) versus the high-temperature _D at T = 13 K previously determined (271±3 K).Work performed under the auspices of the U.S. Department of Energy.     

Adhesion to skin

The failure energy of an adhesive bond can be factorized into two terms, one of which is a dimensionless loss function and the other, the true interfacial bonding energy, ₀. Experimental techniques have been developed to effect a separation of these two terms and thus measure ₀, but they are unsuitable for the pressure-sensitive adhesives used in surgical tapes and dressings. This is because these adhesives flow readily under load. This paper describes an extrapolation technique by which this problem can be resolved. Adhesive peel data are extrapolated both to zero peel velocity and zero load, to give a true threshold value for peeling energy which is independent of temperature. Values of ₀ are given for a natural-rubber based adhesive and substrates of glass and human skinin vivo. For glass ₀ = 28J m^–2 and for normal skin ₀ 14J m-2.     

Anisotropy in the resistive superconducting transition under magnetic fields in single crystal Pb2Sr2Ho0.5Ca0.5Cu3O8

Anisotropie properties of the single crystal Pb₂Sr₂Ho_0.5Ca_0.5Cu₃O₈ have been investigated by measuring the electrical resistivity in theab-plane _ab (H, ,T), which depends on the angle between theab-plane and the magnetic-field direction, in various constant fieldsH perpendicular to the current direction. All the angle-dependent values of _ab (H, ,T) at a constant temperature are scaled to be on one curve as a function of reduced field. The anisotropic parameter (m _c ^* /m _ab ^* )^1/2 is estimated as 12–13, which is larger than that of YBa₂Cu₃O₇ and much smaller than that of Bi₂Sr₂CaCu₂O₈. It has been concluded that the anisotropy does not always depend on the thickness of the blocking layer but seems to depend on the overlap of the electronic wave functions along thec-axis. Anisotropy in the pinning potential has also been discussed from the resistive tail in the temperature dependence of _ab (H,,T).     

Directional dependence of c-plane slip in single crystals of mercuric iodide

An experimental study of plastic deformation in thin single crystals of mercuric iodide (Hgl₂) subjected to (0 0 1) [1 0 0] and (0 0 1) [1 1 0] shear loadings has established a directional dependence to the phenomenon of (0 0 1) orc-plane slip in Hgl₂. The average stressess _c for the onset of yielding were 12.6 psi (86.9 kPa) for (0 0 1) [1 0 0] shear and 16.5 psi (113.8 kPa) for (0 0 1) [1 1 0] shear; the average values of the deformation parameters ₀, interpreted as a bulk yield stress, were 24.7 psi (170.3 kPa) for (0 0 1) [1 0 0] shear and 37.7 psi (259.9 kPa) for (0 0 1) [1 1 0] shear. These values are in agreement with the theoretical relationss _c()=s _c(0)/cos ands ₀()=s ₀(0)/cos, where is the smallest angle between 1 0 0 crystallographic axis and the direction of shear stress applied in the (0 0 1) plane.     

Thermal stresses in a thin circular disc of orthotropic material due to an instantaneous point heat source

Summary In this paper, we have analysed the transient plane thermal stress problem of a circular disc of orthotropic material with instantaneous point heat source. The variation of with time along different radius vectors is exhibited graphically and compared with that of the isotropic case.

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Wärmespannungen in einer dünnen Kreisscheibe aus orthotropem Material zufolge einer punktförmigen instantanen Wärmequelle

Zusammenfassung In dieser Arbeit wurde das instationäre ebene Wärmespannungsproblem einer Kreisscheibe aus orthotropem Material zufolge einer punktförmigen instantanen Wärmequelle untersucht. Die Veränderung von über die Zeit für verschiedene Radien ist graphisch dargestellt und wird mit dem isotropen Fall verglichen.

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Nomenclature r, polar coordinates - T temperature rise - ² ratio of conductivities - ² thermal diffusivity in -direction - J _n Bessel function ofn-th order - t time - p introduced in equation (2) - h heat transfer coefficient - a radius of circular disc - f(r, ) temperature distribution at initial state - r ₀, ₀ a point on the disc - T ₀ strength of point heat source - Dirac delta function - F stress function in two dimensions - ₁, ₂ coefficient of thermal expansion - a ₁₁,a ₁₂,a ₂₂,a ₆₆ elastic constants With 9 Figures     

Analytical and graphical evaluation of local quasi-stable angular points during ion bombardment at oblique incidence

An implied analytical condition, connecting the incidence angles _o and _e between the two intersecting microfacet normals and the ion beam direction, has been inferred for the existence of local quasi-stable intersections (angular points) during ion erosion. This condition, which can also be deduced on the basis of the erosion slowness curve, leads to a higher degree algebraic equation with a parameter, applicable for any dependence S=S (), expressed as an algebraic polynomial expression in cos . A new graphical method for evaluation of orientations _e compatible with a given orientation _o, based on a known polar diagram cursor-type, has also been proposed.     

Spin diffusion coefficient of the A and B phases of liquid3He

The spin diffusion coefficient tensors are calculated in the A and B phases of liquid ³ He in the _{L D} <1 regime by using the Kubo formula approach. The spin wave dispersions are also obtained in the presence of diffusive flow of the normal component. The results agree with Combescot's results qualitatively in the _{L D} <1 regime.     

NMR studies of single crystals of H2. V. NMR anisotropy and order parameter distribution ofX (ortho)≤0.55

We report a study of the NMR line shapes in hcp single crystals of H₂ with ortho concentrationsX0.55 in the regime where there is no longer a transition to a long-range orientationally ordered phase. From the anisotropy of the o-H₂ impurity NMR spectrum at low ortho concentration, reached by ortho-para conversion, the crystal orientation is determined. The second momentM ₂ can be represented by a function of the formM ₂=(X, T)f(cos _Hc ), where _Hc is the angle between the applied magnetic field and the crystalc axis. For a single crystal, the anisotropy functionf(cos _Hc ) is found to be independent of temperature and of ortho concentration within experimental error, and is in very good agreement with predictions based on the first term of the high-temperature expansion ofM ₂ and on other, more general symmetry arguments. An order parameter is defined and the distribution functionP() is calculated from the NMR line shapes under the simplifying assumption that the anisotropy of the order parameter, which gives rise to the observed anisotropy ofM ₂, can be neglected. We giveP() as a function ofX at low temperature, where the line shape is only weakly dependent onT, and as a function ofT at constantX. It is found that the line shapes andP() in both situations evolve continuously and give no hint of a phase transition. These results are discussed in relation to those of magnetic spin-glasses, and it is concluded that the orientational regime in solid H₂, called a quadrupolar glass by previous investigators, cannot be distinguished by symmetry from the orientationally disordered phase that occurs at high temperature.Work supported by NSF grants DMR-81-02993 at Duke University and DMR-79-10153 at the University of Pennsylvania.     

Low-temperature susceptibility of dilute Zn-Mn alloys

The magnetic susceptibility of pure Zn and Zn-Mn alloys containing 12–275 ppm Mn has been investigated in the temperature range 2.7–300 K after different metallurgical treatments. In a 1/X-vs.-T plot the curves for the cold-deformed alloys follow a Curie-Weiss law with a concentration-independent paramagnetic Curie temperature =–1.0 K. The effective moment of Mn isP _eff=4.28 µ _B for these alloys with concentrations above 27 ppm. Annealing of the alloys at temperatures between 200 and 400°C leads to increasing ¦¦ andp _eff.