Diffusion Annealing Temperature Research Articles

Effect of annealing temperature on magnetoresistivity, activation energy, irreversibility and upper critical field of the Cu-diffused MgB2 bulk superconductors

This study manifests the change of the pinning mechanism, superconducting and physical properties of Cu-diffused MgB2 superconductors prepared at different annealing temperature from 650 to 850 °C by means of the magnetoresistivity measurements conducted at several applied magnetic fields in a range of 0–7 T as a function of temperature from 15 to 50 K. The onset (T c onset ) and offset (T c offset ) critical temperatures, activation energies (U0), irreversibility fields (μ0Hirr), upper critical fields (μ0Hc2), residual resistivity ratios (RR), cross-sectional area fractions (AF), penetration depths (λ), coherence lengths (ξ) and electronic mean free path ( $$ \ell $$ ) of the samples are evaluated from the magnetoresistivity curves. Thermally activated flux creep (TAFC) model is used for the determination of the U0 values; likewise, the μ0Hirr and μ0Hc2 values are obtained by resistivity criteria of 10 and 90 % normal-state resistivity, respectively. At absolute zero temperature (T = 0 K), the extrapolation of the μ0Hirr(T) and μ0Hc2(T) curves is used to find the μ0Hirr(0) and μ0Hc2(0) values of the samples. Moreover, the ξ values are deduced from the μ0Hc2(0) values when the λ values are calculated from the Ginzburg–Landau parameter ( $$ \kappa $$ ). It is found that the superconducting and physical properties of the samples improve with the increment of the diffusion-annealing temperature; however, the presence of the magnetic field leading to the decrease of the flux pinning in the samples causes the reduction of these properties. Namely, the T c onset and T c offset values are found to increase from 38.4 to 39.3 K and 36.9 and 38.3 K with the enhancement in the diffusion-annealing temperature at zero filed. Similarly, the U0 values increase significantly with the increase of the annealing temperature. In fact, the U0 of 9,162 K belonging to the sample annealed at 850 °C is determined to be the maximum activation energy value. On the other hand, the minimum T c onset of 30.9 K, T c offset of 27.6 K and U0 of 1,365 K at 7 T applied magnetic field are obtained for the pure sample, indicating that the sample annealed at 850 °C obtains much stronger flux pinning, better crystallinity and connectivity between grains compared to the other samples prepared. Based on these results, the superconducting and physical properties of the MgB2 superconductors produced in this work are observed to enhance with the increase of the diffusion-annealing temperature as a result of the improvement of pinning abilities, crystallinity and connectivity between grains. The magnetic field and temperature dependence of the activation energy are also discussed.

Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors

This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB2 superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T c ) increase with increasing the diffusion-annealing temperature from 650 to 850 °C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850 °C. As for the XRD results, all the samples contain the MgB2 phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81 × 10−8 to 4.69 × 10−7 cm2 s−1 as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D = 3.75 × 10−3 exp (−1.15 ± 0.10 eV/k B T) and the corresponding activation energy of copper in MgB2 system is found to be about 1.15 eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.

Influence of Diffusion-Annealing Temperature on the Physico-Mechanical Properties of Au-doped Bi-2223 Superconductors

In order to investigate the influence of Au doping and diffusion-annealing temperature on the mechanical and superconducting properties of Bi-2223, Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of gold diffusion during sintering from an evaporated gold film on pellets. The investigation consisted of scanning electron microscopy, dc resistivity and hardness measurements. Electrical-resistivity measurements indicated that the room-temperature resistivity value decreased with decreasing diffusion-annealing temperature from 830 to 500 °C and these samples (G830, G800, G750, G700, G600 and G500) show the resistive behavior above the onset critical transition temperature with the zero-resistivity transition temperatures of 104 K, 80 K, 98 K, 95 K, 102 K and 103 K, respectively. To investigate mechanical properties of the samples, we have measured the diagonal length as a function of test load in the range of 0.245–2.940 N. Mechanical properties (microhardness, Young’s modulus, yield strength and fracture toughness) of the samples are found to be load and diffusion-annealing temperature dependent. In addition, we have calculated the load independent hardness, Young’s modulus, yield strength, and fracture toughness of the samples. The possible reasons for the observed changes in superconducting and mechanical properties due to Au diffusion and diffusion-annealing temperature were discussed.

Formation of manganese solid solutions in single crystals of ZnGeP2

Process of the solid-phase diffusion of manganese into single crystals ZnGeP2 are investigated by electron paramagnetic resonance and X-ray element microanalysis. Conditions for formation of a solid solution with Mn2+ concentration of 1018 cm-3 were found. A diffusion coefficient of manganese in single crystal of ZnGeP2 at a diffusion annealing temperature was determined.

EDXRF measurements on gold diffusion-doped Bi 1.8Pb 0.35Sr 1.9Ca 2.1Cu 3O y

Gold (Au) diffusion in superconducting Bi 1.8Pb 0.35Sr 1.9Ca 2.1Cu 3O y was investigated over the temperature range 500–800 °C by the energy dispersive X-ray fluorescence (EDXRF) technique. It is found that the Au diffusion coefficient decreases as the diffusion-annealing temperature decreases. The temperature dependences of Au diffusion coefficient in grains and over grain boundaries are described by the relations D 1=6.7×10 −5exp(−1.19 eV/k BT) and D 2=9.7×10 −4exp(−1.09 eV/k BT), respectively. The diffusion doping of Bi-2223 by Au causes a significant increase of the lattice parameter c by about 0.19%. For the Au-diffused samples, dc electrical resistivity and transport critical current density measurements indicated the critical transition temperature increased from 100 to 104 K and the critical current density increased from 40 to 125 A cm −2, in comparison with those of undoped samples. From scanning electron microscope (SEM) and X-ray diffraction (XRD) measurements it is observed that Au doping of the sample also improved the surface morphology and increased the ratio of the high- T c phase to the low- T c phase. The possible reasons for the observed improvement in microstructure and superconducting properties of the samples due to Au diffusion are also discussed.

Activation energy U (H) and pinning behavior of Yb‐impurity‐diffused YBa2Cu3O7–x

AbstractSuperconducting Y123 samples were prepared by the solid‐state reaction (SSR) method. To get a layer of Yb (thickness ∼4 μm) on the surface of one side of the sample an ultrahigh‐vacuum electron‐beam deposition system was used and Yb diffusion in Y123 was carried out thermally. The energy dispersive X‐ray fluorescence technique (EDXRF) was used for the determination of the concentration of Yb atoms in the diffusion regions of Y123 samples. It was found that when the diffusing‐annealing temperature increased the transition became much sharper and the sharpest transition was observed for the sample diffused at 900 °C. The activation energy of all samples was estimated from the resistivity curves using the TAFF model. It has been revealed that the pinning properties and activation energy improve when the diffusion‐annealing temperature increases for a convenient temperature and also the activation energies of Yb‐diffused samples are larger than that of an undoped Y123 sample. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gadolinium diffusion-doping for enhancing activation energy in superconducting YBa2Cu3O7−x

Abstract The resistance transitions of Gd-diffused polycrystalline Y123 samples have been measured as a function of temperature and magnetic field. It is deduced from experimental results that the activation energy increases when the diffusion annealing temperature increases and also the activation energy of Gd-diffused samples are larger than that undoped Y123 sample. The magnetic field dependence of U follows a power law, i.e. U ∝ H − α , with the values of α are 0.42, 0.56 and 0.61, respectively, for pure Y123, and Gd-diffused Y123 at 800 and 900 °C. The changing of α values from 0.42 to 0.61 imply that the thermally activated dissipative resistivity is directly associated with pinning mechanism changes from intrinsic planar defects pinning to extrinsic point defects pinning because of large Gd content into Y123 sample by the means of diffusion annealing temperature increasing. In this paper, the possible reasons responsible for the effect of Gd-diffusion on the pinning behaviors are discussed.

Improvement of the matrix and the interface quality of a Cu/Al composite by the MARB process

Abstract The matrix accumulative roll bonding technology (MARB) can improve the matrix performance of metal composite and strengthen the bonding quality of the interface. In this research, for the first time, the technology of MARB was proposed. A sound Cu/Al bonding composite was obtained using the MARB process and the bonding characteristic of the interface was studied using scanning electricity microscope (SEM) and energy-dispersive spectroscopy (EDS). The result indicated that accumulation cycles and diffusion annealing temperature were the most important factors for fabricating a Cu/Al composite material. The substrate aluminum was strengthened by MARB, and a high quality Cu/Al composite with sound interface was obtained as well.

Mössbauer investigation of Sn diffusion and segregation in grain boundaries of polycrystalline Nb

The parameters of nuclear γ resonance (Mossbauer) spectra on 119mSn nuclei inserted into grain boundaries of polycrystalline Nb have been determined at the annealing temperatures of 680 to 994 K [0.25–0.36 melting temperature (T m)]. Two components are observed in the nuclear emission γ resonance spectra at all of the annealing temperatures considered. One of them (component 1) is suggested to result from the 119mSn atomic probes localized in grain boundary cores, while the other one (component 2) corresponds to that located in the near-boundary areas. Diffusion annealing temperature dependences of both components parameters have been analyzed. The coefficients and enthalpy of Sn grain-boundary segregation are determined based on this analysis, as well as the ratio of the diffusion pumping zone extension to the grain boundary width and the enthalpy of the atomic probes “pumping” from grain boundaries into the bulk.

The effects of CeF3 doping on the photoluminescence of Si nanocrystals embedded in aSiO2 matrix

The effects of CeF3 doping on the photoluminescence (PL) of Si nanocrystals embedded in aSiO2 matrix, assignedas nc-Si:SiO2, have beenstudied. The nc-Si:SiO2 sample was prepared by means of reactive evaporation followed by thermal annealing, andCeF3 doping was conducted via thermal diffusion. It is found that the doping ofCeF3 is able to enhance the PL intensity of nc-Si by a factor as large as 3.7. With the increasingdoping concentration, the degree of PL intensity enhancement increases until amaximum is reached, and then it drops down. This trend also holds for the PLintensity enhancement versus the diffusion annealing temperature. A continuousredshift of the PL peak was observed with the increasing doping concentration anddiffusion annealing temperature. Beyond a certain concentration or temperature, thePL peak starts to shift back towards shorter wavelengths. The doping effects onthe PL intensity were explained by a model of electron transfer from Ce ionsto nc-Si, while the trends of PL peak shift were accounted for with the help ofa previous model referring to the size distribution of nc-Si crystallites versusnc-Si:SiO2 film thickness (Fang et al 2004 Nanotechnology 15 494); the peak shift was also related tothe chemical reaction between Ce and Si.

Behavior of impurity copper in ZnGeP2 single crystals with diffusion doping

Results from a study of electrophysical and luminescent properties of zinc-germanium diphosphide single crystals, diffusion doped with copper, are presented. The nature of the dominant defects formed upon copper diffusion in ZnGeP2 is determined using a thermodynamic analysis of defect formation processes in ZnGeP2 and a ZnGeP2: Cu solid solution performed within the framework of the quasichemical analysis method. It is demonstrated that by choosing the copper diffusion method the hole concentration in the ZnGeP2 can be varied over the range 1012−1016 cm−3. A retrograde character was observed in copper solubility in ZnGeP2 compounds. Defect formation processes in ZnGeP2 upon copper diffusion depend on the degree of atomic ordering in the cation sublattice at the diffusion annealing temperature.