Frequency Response of AC Susceptibility in Melt Textured YBCO Superconductors

We have reviewed the scaling relations for frequency dependent AC susceptibility proposed by Lee. et al. and other contributions. Based on vortex glass analysis, we derived a scaling equation for the peak temperature of the imaginary part and ac magnetic field frequency f. The peak temperature T_p is found to obey: T_p = Cf^1/(v(z–1))+T_g, where C is a constant, and T_g is the vortex glass temperature. The scaling relationship was applied to our melt textured YBCO superconductors, which was found in good agreement with the experimental data.     

Crystallization kinetics of selenium-tellerium glasses

Bulk glasses of the compositions Se₇₀Te₃₀ and Se₈₀Te₂₀ were prepared by the melt quenching technique. Differential thermal analyses were performed at different heating rates. The values of the glass transition temperature,T _g, the crystallization temperature,T _c, and the peak temperature of crystallization,T _p, were found to depend on the composition and the heating rate. The activation energy for the glass transition,E _i, as well as the activation energy for crystallization,E _c, were evaluated from the heating rate dependence ofT _g andT _p. The crystallization mechanism was examined through analysis of the data under non-isothermal conditions. The results indicated that surface crystallization is dominant for both compositions.     

Transport Properties of a Tl-2201 Film Close to the Critical Temperature: The Vortex Glass Transition

We have studied the I-V characteristics of a Tl-2201 film at zero field. In the regime in which flux creep is the dominant dissipation mechanism, the J _c -T curve is divided into two parts at a temperature T _g (about 82 K), close to the critical temperature (84 K). The I-V characteristics around T _g are well described using a flux creep model. For T>T _g , J _c /J _c (0) =0.445x(l-0.525t-0.5t ² ); for T _g , J _c /J _c (0) = 0.9x(1-0.595t-0.44t ² ). Differential resistance (dV/dI) as a function of the measuring current shows a change in curvature close to T _g . The I-V curves collapsed nicely into two branches by plotting (V/I)/|T–T _g | ^v(z-1) vs. (I/T)/|T _g –T| ^2v , indicating a current–reduced vortex glass transition.     

Internal friction in Se-Sb glasses

The internal friction,O ^–1, as a function of temperature has been investigated for Se_100–x Sb _x systems, wherex=7.5, 12.5 and 17.5 at%, using the magnetostrictive pulse-echo method in the range of vibrational frequencies 50–100 kHz. Two well-defined peaks appeared, characterizing this glass. The first peak covers the temperature range 320–330 K, where the peak position has been shifted to the higher temperature as Sb content increases. This peak indicates the glass transition temperature,T _g, of the tested glassy samples. The second peak was detected in the temperature range 360–378 K. The position of this peak has been shifted to a lower temperature as Sb content increases. This peak is attributed to the crystallization temperature,T _c, of each glassy sample tested. The peak height of both of the above peaks decreased as the Sb content increased. Also, the appearance of these two peaks was affected by annealing.     

Dielectric properties of solution-grown-undoped and acrylic-acid-doped ethyl cellulose

Dielectric capacities and losses were measured, in the temperature (50–170°C) and frequency (01–100 kHz range), for undoped and acrylic acid (AA) doped ethyl cellulose (EC) films (thickness about 20 μm) with progressive increase in the concentration of dopant in the polymer matrix. The variation of capacity with temperature is attributed to thermal expansion in the lower temperature region to the orientation of dipolar molecules in the neighbourhood of glass transition temperature (T _g) and random thermal motion of molecules aboveT _g. The dielectric losses exhibit a broad peak. Doping with AA is found to affect the magnitude and position of the peak. AA is found to have a two-fold action. Firstly, it enhances the chain mobility and secondly, it increases the dielectric loss by forming charge transfer complexes.     

Dynamic mechanical analysis of carbon/epoxy composites for structural pipeline repair

The viscoelastic behavior of a carbon fiber/epoxy matrix composite material system used for pipeline repair has been evaluated though dynamic mechanical analysis. The effects of the heating rate, frequency, and measurement method on the glass transition temperature (T_g) were studied. The increase in T_g with frequency was related to the activation energy of the glass transition relaxation. The activation energy can be used for prediction of long term performance. The measured tan delta peak T_g’s of room temperature cured and post-cured composite specimens ranged from 60 to 129 °C. Analysis of T_g data at various cure states was used to determine use temperature limits for the composite repair system.     

Thermal Relaxation and High Temperature Creep of Zr55Cu30Al10Ni5 Bulk Metallic Glass

The free volume model is applied to isothermal relaxation and hightemperature creep. For this analysis, the time dependent flow behaviourof Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass (BMG) near the glass transition temperature (T _g ) is expressed as a trade off between stress inducedgeneration and diffusion controlled annihilation of free volume. Thestrain rate-stress relation over a wide strain rate-range (10^–7to 10^–2 s^–1) was established for three different temperatures near T _g . It was found that the thermal relaxation behaviour and creep kinetics arecontrolled by the mobility of atoms with an activation energy of 161 kJ/mol.     

Scaling Behavior and Estimation of Activation Energy of Polycrystalline RuSr2GdCu2O8 Superconductor from AC Susceptibility Measurements

In this study, the measured curves of AC susceptibility (ACS) components, χ′(T) and χ″(T), of polycrystalline RuSr₂GdCu₂O₈ (Ru-1212) superconductor were scaled onto a single curve using the peak temperature of its imaginary part (T _p) as the scaling parameter for various AC field amplitudes from 0.5 to 24 G. The dependence of the AC magnetic field amplitude on T _p is scaled as: H _ac ～ (1?T _p/T _c)^2.25. Similarly, the current density J _c, extracted from the AC field amplitude is also scaled as: J _c ～ (1 ? T _p/T _c)^2.25. The dependencies of T _p on frequency and AC field amplitude are also investigated and the time parameter t ₀ of the order of 10^?8 s is estimated from the dependence of T _p on frequency. The dependencies of activation energy on temperature, T, and the field amplitude, H _ac, are obtained from the Arrhenius-like semilog plot of frequency (ν) and T _p. Such dependencies on temperature and field amplitude can be described by a scaling law of the form: U(H _ac,T) = U ₀[1 ? T/T _p]H _ac ^?0.17.     

Scaling Behavior and Estimation of Activation Energy of Polycrystalline RuSr2GdCu2O8 Superconductor from AC Susceptibility Measurements

In this study, the measured curves of AC susceptibility (ACS) components, (T) and (T), of polycrystalline RuSr₂GdCu₂O₈ (Ru-1212) superconductor were scaled onto a single curve using the peak temperature of its imaginary part (T _p) as the scaling parameter for various AC field amplitudes from 0.5 to 24 G. The dependence of the AC magnetic field amplitude on T _p is scaled as: H _ac (1–T _p/T _c)^2.25. Similarly, the current density J _c, extracted from the AC field amplitude is also scaled as: J _c (1 – T _p/T _c)^2.25. The dependencies of T _p on frequency and AC field amplitude are also investigated and the time parameter t ₀ of the order of 10^–8 s is estimated from the dependence of T _p on frequency. The dependencies of activation energy on temperature, T, and the field amplitude, H _ac, are obtained from the Arrhenius-like semilog plot of frequency () and T _p. Such dependencies on temperature and field amplitude can be described by a scaling law of the form: U(H _ac,T) = U ₀[1 – T/T _p]H _ac ^–0.17.     

Theoretical determination of the lattice dynamical properties of the mercury based superconductor HgBa2CuO4

A theoretical study of the lattice dynamical properties for the high temperature superconductorH _gBa₂CuO₄ is made within the framework of the shell model. A frozen-phonon first principles determination of frequencies and eingevectors of the Raman active modes is also made. We compare these results with the recent Raman and neutron scattering experimental work and use them to obtain insight for a possible clarification of mode assigment. The origen of the 570 cm^–1 shoulder peak that appears in the low frequency side of the oxygenA _1g peak is discussed althought an unambiguous distinction of thisT _1g like defect mode is not possible at present.     

Calorimetric and optical study of amorphous Se85 − xTe15Bix glassy alloy

Bulk samples of Se_85 − xTe₁₅Bi_x (where x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained by melt quenching technique. Differential scanning calorimetric (DSC) technique has been applied to determine the thermal properties of Se-rich Se_85 − xTe₁₅Bi_x glassy alloys in the glass transition and crystallization regions at four heating rates (5, 10, 15, 20 K min^− 1). The glass transition temperature (T_g) and peak crystallization temperature(T_p) are found to shift to a higher temperature with increasing heating rate. With Bi addition, the value of (T_g)increases. (T_p) is found to increase as Bi is introduced to the Se-Te host, however further increase in Bi concentration is responsible for the reduction of. Thin film of bulk samples are deposited on glass substrate using thermal evaporation technique under vacuum for optical characterization. Optical band gap is estimated using Tauc's extrapolation and is found to decrease from 1.46 to 1.24 eV with the Bi addition.     

Structure-properties relationships for densely crosslinked epoxide-amine systems based on epoxide or amine mixtures

Four series of samples based on epoxide mixtures crosslinked by aromatic diamines or single epoxides crosslinked by amine mixtures were studied by dynamic thermomechanical analysis, differential scanning calorimetry and heat deflection temperature measurements. The glass transition temperature (T _g) was found to increase with the crosslink density in each series, but was independent of the cohesive energy or hydrogen bonding densities. A previously established method ofT _g prediction was shown to be applicable to these systems. In one series, (diglycidyl ether or bisphenol A/triglycidyl derivative ofp-amino phenol/diamino diphenyl methane), a phase separation occurred during the sample preparation. TheT _g-structure relationships were used to determine the phase composition.     

Thermal stress hysteresis and stress relaxation in an epoxy film

Thermal cycling of an epoxy coating on silicon through the glass transition temperature (T _g) revealed a large stress hysteresis on the first thermal cycle through T _g and a change in the stress–temperature slope at T _g resulting from the change in the epoxy elastic properties due to the glass transition. This stress hysteresis was not observed on subsequent thermal cycles through T _g. However, after the coating was annealed (aged) below T _g (for hours or longer)—during which the stress relaxed exponentially with time—the stress hysteresis returned. The magnitude of stress hysteresis, on cycling through T _g, was found to correlate to the magnitude of long-time relaxation that occurred during annealing at temperatures below T _g.     

Thermal characteristics and crystallization kinetics of tellurite glass with small amount of additive As<Subscript>2</Subscript>O<Subscript>3</Subscript>

The crystallization kinetics of the TeO₂/TiO₂/As₂O₃ glassy system was studied under nonisothermal conditions. The method was applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. In addition, two approaches were used to analyze the dependence of glass transition temperature (T _g) on the heating rate (β): One is the empirical linear relationship between (T _g) and (β); The other approach is the use of straight line from the plot of ln( T_\textg² /b ) \textvs . 1/T_\textg \ln \left( {T_{\text{g}}^{2} /\beta } \right)\,{\text{vs}} .\,1/T_{\text{g}} for evaluation of the activation energy for glass transition. The crystallization results are analyzed, and both the activation energy of crystallization process and the crystallization mechanism are characterized.     

Crystallization study of Te-Bi-Se glasses

Crystallization studies are carried out under non- isothermal conditions with samples heated at several uniform rates. The dependence of the glass transition temperature (T_g), the crystalline temperature (T_c) and the peak temperature of crystallization (T_p) on the composition and heating rate (β) has been studied. For a memory/switching material, the thermal stability and ease of glass formation are of crucial importance. The glass transition temperature, T_g, increases slightly with the variation of Bi content. From the heating rate dependence of T_g, the activation energy for glass transition (E_t) has been evaluated. The results are discussed on the basis of Kissinger’s approach and are interpreted using the chemically ordered network model (CONM).     

Ultrasonic velocities and thermal expansion coefficients of amorphous Se80Te20 and Se90Te10 alloys near glass transitions

Precise measurements of the ultrasonic velocities and thermal expansivities of amorphous Se₈₀Te₂₀ and Se₉₀Te₁₀ alloys are reported near the glass transition. The samples are produced by liquid quenching. The longitudinal and transverse velocities are measured at 10 MHz frequency using the McSkimin pulse superposition technique. The thermal expansivities,, are measured using a three-terminal capacitance bridge. The-values show a sharp maximum near the glass transition temperature,T _g. The ultrasonic velocities also show a large temperature derivative, dV/dT nearT _g. The data are discussed in terms of existing theories of the glass transition. The continuous change in shows that the glass transition is not a first-order transition, as suggested by some theories. The samples are found to be deformed by small loads nearT _g. The ultrasonic velocities and dV/dT have contributions arising from this deformation.     

NMR Study on the Electronic Structure of the Vortex State in HTSC

By using spatially-resolved NMR method, we observed nuclear spin-lattice relaxation rate (1/T ₁) of the vortex state to probe antiferromagnetic correlations at the vortex core. We found that the temperature dependence of 1/T ₁ shows a peak, which results from a local antiferromagnetic ordering of Cu spins in the vortex core.     

Er- and Nd-doped yttrium aluminosilicate glasses: Preparation and characterization

The undoped, and Nd-, Er-doped low silica high alumina yttrium aluminosilicate (YAS) glasses were prepared by flame synthesis in the form of transparent glass microbeads with diameters ranging from a few to several tens of micrometers. The silica content ranged between 5 and 20 mol.%. The prepared glass microbeads were characterized by optical microscopy, SEM XRD, FT-IR and UV–VIS–NIR spectroscopy. The glass forming ability of glasses, expressed in terms of the difference between the glass transition temperature, T_g, and the onset of crystallization, T_x, improved with increasing silica content. Doping of YAS15 glass with neodymium or erbium at the level of 1–5 mol.% leads to decrease of both the T_g and T_x. However, the glass forming ability was not affected. The UV–VIS–NIR reflectance spectra in the spectral range from 300 to 1800 nm shows characteristic absorptions, due to the optically active Nd³⁺ and Er³⁺ ions in the host glass.     

Crystallization kinetics and structure of (TeO2-TiO2-Fe2O3) Glasses

Crystallization kinetics and structure of (85TeO₂ + 15TiO₂) and (85TeO₂ + 10TiO₃ + 5Fe₂O₃) glasses are studied using differential scanning calorimetry DSC, IR spectroscopy and XRD. DSC curves in the temperature range from 50 to 525°C with different heating rates from 10 to 40°C/min are used to study the crystallization behavior of the glasses and effects of different heating rates on the glass transition and crystallization temperatures (T_g and T_p). The activation energies of the glass transition and crystallization processes were determined from the shift of T_g and T_p with the heating rates using Kissinger's formula. Effects of the polymorphic nature of TeO₂ on the crystallization mechanisms are discussed and the phases crystallized during the DSC process were identified by XRD. IR spectra in the frequency range (500–4000 cm^-1 ) are measured and possible coordination states of the constituent oxides are discussed for heat-treated and untreated glasses.     

Interplay Between Vorticity and Chirality Inside the Vortex Core in Chiral p-Wave Superconductors

The vortex core in chiral p-wave superconductors exhibits various properties owing to the interplay between the vorticity and chirality inside the vortex core. In the chiral p-wave superconductors, the site-selective nuclear spin-lattice relaxation rate T ^–1 ₁ is theoretically studied inside the vortex core within the framework of the quasiclassical theory of superconductivity. T ^–1 ₁ at the vortex center depends on the sense of the chirality relative to the sense of the magnetic field. The effect of a tilt of the magnetic field upon T ^–1 ₁ is investigated. The effect of the anisotropy in the superconducting gap and the Fermi surface is then investigated. The result is expected to be experimentally observed as a sign of the chiral pairing state in a superconducting material Sr₂RuO₄.