Pre-annealing Process Research Articles

$J_{\rm c}$ Enhancement in Nano-${\rm Si}_{3}{\rm N}_{4}$ Doped ${\rm MgB}_{2}/{\rm Fe}$ Tapes Prepared by a Short Pre-Annealing and Intermediate Rolling Process

Using our newly developed short pre-annealing and intermediate rolling process, the property of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Fe tapes doped with nano-Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> particles was further improved. The highest J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> value at 10 T and 4.2 K reached 6310 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the sample doped with 1% nano-Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> by using our new process, which was obviously higher than that of 4550 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> obtained in the sample made via the conventional in situ PIT process. Furthermore, it was found that the improvement of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> became smaller with increasing the doping concentration of nano-Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> particles. This confirmed that our new process contributed to the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> enhancement mainly through increasing the core density and connectivity. Adding more nano-Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> introduced more impurities at the grain boundaries, which made our new process less effective.

Preannealing effect on ordering transformation and magnetic properties of CoPt thin films

Single layer CoPt thin films with thicknesses from 30to100nm were sputtered on glass substrates. A preannealing at 250°C for 80min was applied to the samples, before ordering treatment at 700°C for 10min. This preannealing process resulted in a 33%–65% decrease in coercivity and 23%–55% decrease in volume fraction of order phase f0. Results of morphology investigation showed that the preannealing increases the surface roughness, which mainly results from the elimination of defects. Structural results further suggest that the eliminated defects are mostly low dimensional, such as dislocations or vacancies. It can thus be concluded that those low dimensional imperfections in the CoPt films play an enhancing role in ordering transformation process.

Quantitative determination of depth carrier profiles in ion-implanted Gallium Nitride

We studied the electrical activation of Si+ ions implanted at multiple energies (80 and 180keV) and with a total fluence up to 2.7×1014cm−2 in heteroepitaxial GaN films on sapphire. Calibrated scanning capacitance microscopy (SCM) is proposed as a method to measure the depth carrier profile after high temperature annealing (1100–1200°C). Si electrically active fractions of 18% and 36% were obtained after low ramp rate furnace annealing at 1100 and 1200°C, respectively. Interestingly, the dopant activation was significantly improved to 63% in the case of a rapid pre-annealing process at 1100°C before the 1200°C furnace annealing process. Furthermore, the ionised carrier fluence obtained by Hall measurements at room temperature exhibits a significant improvement for the 1100°C RTA pre-annealed sample. This value is in good agreement with the ionised fluence calculated from the active Si profile from SCM, considering a ∼20meV ionisation energy for Si donors in GaN.

Enhancement of the critical current density of Ag-sheathed Bi-2223 tapes by optimized pre-annealing and pre-rolling process

The effect of pre-annealing and pre-rolling (an initial rolling deformation prior to pre-annealing) on the final engineering critical current density Je of Ag-sheathed Bi-2223 tapes has been investigated. The optimization of pre-annealing process was found to be dependent on annealing temperature much more than on oxygen partial pressure or soaking time. The highest Je has been achieved for pre-annealing at 790°C for 20h in a flowing 8.5% O2-balance N2 atmosphere. Optical microscope and XRD rocking curve analysis show that pre-rolling improved the homogeneity of the tapes, reduced the sausaging effect and improved the texturing of the superconducting phase. All these effects strengthen the grain connectivity and further enhance the Je value of the tapes. Too large a pre-rolling reduction, however, decreased the Je owing to the introduction of more cracks that cannot be completely healed in subsequent heat treatment.

Comparison of visible photoluminescence from Si ion-irradiated SiO 2/Si/SiO 2 films fabricated by ion beam sputtering deposition and electron beam evaporation

The SiO 2/Si/SiO 2 thin films were fabricated by ion beam sputtering deposition and electron beam evaporation, respectively. Photoluminescence was measured from the samples deposited, annealed at high temperature, and/or irradiated by Si ions. Even though the photoluminescence associated with Si nanocrystals was obtained from the samples prepared by two kinds of deposition method; in the case of sample deposited by electron beam evaporation, a pre-annealing process was required to get the photoluminescence spectrum contrary to sample made by ion beam sputtering deposition. After the same process was performed with the samples deposited by two deposition methods, the photoluminescence from the samples has been measured differently each other. We discuss the observed difference of the photoluminescence in terms of defect-related photoluminescence and electron spin resonance.

펄스레이저 증착법으로 제작된(Pb0.72,La0.28)Ti0.93O3박막의 수소후열처리에 관한 전기적 특성 연구

Dielectric thin films of (P <TEX>$b_{0.72}$</TEX>,L <TEX>$a_{0.28}$</TEX>) <TEX>$Ti_{0.93}$</TEX> <TEX>$O_3$</TEX> (PLT(28)) have been deposited on Pt(111)/Ti/ <TEX>$SiO_2$</TEX>/Si(100) substrates in-situ by pulsed laser deposition using different annealing and deposition Processes. We have investigated the effect of hydrogen annealing on the ferroelectric properties of PLT thin films and found that the annealing process causes the diffusion of hydrogen into the ferroelectric film resulting in the destruction of polarization. We have tried to form the film by a two-step deposition process In order to improve electrical property. Two-step process to grow PLT films was adopted and verified to be useful to enlarge the grain size of the film and to reduce the leakage current characteristics. Structural properties and electrical properties including dielectric constant, ferroelectric characteristics, and leakage current of PLT thin films were shown to be strongly influenced by grain size. The film deposited by using two-step Process including pre-annealing treatment has a strongly(111) orientation. However, the films deposited by using single -step process with hydrogen annealing process show the smallest grain size. The film deposited by using two-step process including pre-annealing treatment shows the leakage current density of below 10<TEX>$^{-7}$</TEX> A/c <TEX>$m^2$</TEX> for the field of smaller than 100 kV/cm. However, the films deposited by using single-step process with hydrogen annealing process and pre-annealing process show worse leakage current density than the film deposited by using two-step process including pre-annealing treatment.tment.

Local J/sub C/ and microstructures of multilayer Bi-2212 composite tape

We investigated the local J/sub C/ and microstructures of Bi-2212 multilayer tapes. Multilayer tapes were prepared by wrapping four dip-coated sheets with silver foil. These tapes were fabricated with a melt-solidification method with a Pre-Annealing and Intermediate Rolling (PAIR) process. The local J/sub C/ distribution along the transverse direction of the tapes was determined in a nondestructive manner in which a magnetic field with a steep gradient was applied at 77 K, and the I/sub C/ was measured. The microstructures of the superconducting oxide layers were observed by using an optical micrograph and an SEM micrograph. Bi-2212 superconducting oxide layers existed on silver substrates homogeneously, and the silver/oxide interfaces were almost smooth along the silver substrates. From the J/sub C/-profile, J/sub C/ values at the middle region on the tape were low in comparison with the J/sub C/ values in the edge regions. The depression of the J/sub C/ values around the middle region was due to the overlapping of silver foil and, hence, the inferior microstructure.

Investigation of the microstructure of ramp-typeYBa2Cu3O7-δ structures

We studied the morphology of ramps in YBa2Cu3O7-δ films and, subsequently, the barrier layer. The ramps have beenfabricated by Ar ion beam milling using standard photoresist masks. SEM andAFM showed the formation of tracks along the slope of the ramp, originatingfrom the irregular shape of the edge of the photoresist mask. A proposedmodified reflowed resist and pre-annealing process show a significantly smootherramp surface, important for the fabrication of reproducible Josephson junctions.

The influence of preannealing treatment on the exothermic behavior and magnetic properties of Fe 73.5Cu 1Nb 3Si 13.5B 9 alloy

The preannealing process has been tried to resolve the overheating problem of the amorphous precursors Fe 73.5Cu 1Nb 3Si 13.5B 9 ribbons when they are heat-treated under the optimum annealing process. The concentrating release of latent heat for the primary crystallization of Fe 73.5Cu 1Nb 3Si 13.5B 9 ribbons can be reduced by fractional crystallization in the preannealing process. Quantitatively, a quarter of the latent heat can be released in advance at preannealing temperature 743 K for 30 min. The subsequent measurement of the soft magnetic properties indicates that the ribbons heat-treated first under the proper preannealing and then under the final annealing process (813 K for 60 min) still exhibit excellent soft magnetic properties.

Relationship between Bi 2Sr 2CaCu 2O x layer thickness and Jc enhancement by pre-annealing and intermediate rolling process

Pre-annealing and intermediate rolling (PAIR) process enables one to fabricate Bi 2Sr 2CaCu 2O x (Bi-2212)/Ag tapes with high transport J c>5.0×10 5 A/cm 2 at 4.2 K, 10 T. We study the relationship between thickness of Bi-2212 layer and J c enhancement by PAIR process for monolayer Bi-2212/Ag tapes. J c enhancement by PAIR process is more significant for thinner Bi-2212 layer. For Bi-2212 layer less than 10 μm thick, oxide J c (4.2 K, 10 T) around 4.0 and 1.6×10 5 A/cm 2 are obtained for PAIR and no-PAIR samples, respectively, however, a large variation of J c is seen for both series of samples in this thickness range. Good reproducibility of J c is seen for the samples with the Bi-2212 layer around 20 μm with oxide J c (4.2 K, 10 T) around 3.2×10 5 A/cm 2. PAIR samples show smaller J c variation than no-PAIR samples. J c enhancement by PAIR process diminishes with increasing Bi-2212 layer thickness and disappears at the thickness around 50 μm. PAIR process produces Bi-2212 layer with small variation of thickness (2–8% along the tape length and 2–19% across it), however, large variation of thickness (4–24% along the tape length and 30–80% across it) remains in no-PAIR samples. PAIR process has a large effect to improve the macroscopic homogeneity of Bi-2212 layer. This is supposed to be one of the reasons for the large J c enhancement achieved by PAIR process.

Performance at 10–50 K of Bi-2212/Ag multilayer tape fabricated by using pre-annealing and intermediate rolling process

High-transport critical current density ( J c-oxide)>500 kA/cm 2 at 4.2 K, 10 T can be obtained for Bi-2212/Ag tapes fabricated by using pre-annealing and intermediate rolling (PAIR) and melt-solidification process. In this paper, we report high-temperature properties of PAIR-processed Bi-2212/Ag multilayer tape in order to show their potential for practical applications operated at cryocooling temperatures. Magnetic field dependence and angular dependence of critical current ( I c) are investigated at temperatures ranging 10–50 K by using helium gas cooling and liquid neon. Field-temperature curves for I c=0.2 and 2.0 A are also determined in order to show the approximation of the irreversible field. High-temperature performance of the tape is attractive to consider future applications. For example, the best sample carries I c=267 A (engineering- J c=303 A/mm 2, J c-oxide=151 kA/cm 2) and 92 A (104 A/mm 2, 52 kA/cm 2) at 27.1 K (in liquid neon), in magnetic fields (parallel to the tape surface) of 2 and 10 T, respectively. Engineering- J c of 100 A/mm 2 is obtained even in the perpendicular field of 0.5 T at 27.1 K.

Optimization of melt-processing temperature and period to improve critical current density of Bi 2Sr 2CaCu 2O x/Ag multilayer tapes

We have studied the effect of melt-processing temperature and period on microstructure and critical current density ( J c) of Bi-2212/Ag multilayer tapes. High J c values of 4.0×10 5 A/cm 2 with the dispersion <10% at 4.2 K, 10 T are obtained in the tapes fabricated by using the combination of preannealing and intermediate rolling (PAIR; preannealing at 850°C for 1 h and 25% intermediate rolling) process and melt-process (at temperature between 875 and 888°C for 1 h) and slow-cooling process. This fabrication procedure enables one to obtain high J c values by using the melt process with a wider and lower temperature range for a longer period than the conventional melt process. Excellent reproducibility in J c value and wide range of optimal processing parameters are expected to lead to more efficient production of long tapes with high uniformity. It is applicable for fabricating large Bi-2212/Ag coils and/or magnets with high quality for practical applications.

Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x//Ag multilayer tapes with J/sub c/ (4.2 K, 10 T) of 500,000 A/cm/sup 2/ by using PAIR process

We developed PAIR (pre-annealing and intermediate rolling) process, which is a fabrication procedure for Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/(Bi-2212)/Ag composite tapes, in order to improve their superconducting properties. PAIR process is the combination of pre-annealing (PA) and subsequent intermediate rolling (IR) processes and is performed prior to a melt-solidification process. By performing the PAIR process, Bi-2212 grain alignment and intergrain connectivity are much improved and a large J/sub c/ enhancement can be expected for Bi-2212/Ag conductors. We study the effects of pre-annealing and intermediate rolling processes on microstructure and superconducting properties of the Bi-2212/Ag multilayer tapes fabricated by the oxide-painting and lamination method. The results show that J/sub c/ has been increased strongly by performing pre-annealing at 1133 K in oxygen (1 atm) and intermediate rolling with 25% deformation. PAIR processed samples have transport J/sub c/-oxide (4.2 K, 10 T) exceeding 5.0/spl times/10/sup 5/ A/cm/sup 2/. Whereas J/sub c/-oxide for the samples melt-solidified without PAIR process remains 3.0/spl times/10/sup 5/ A/cm/sup 2/. The enhancement of J/sub c/ is assigned to the microstructure with high grain alignment and uniformity, as well as the improvement in grain connectivity achieved by the PAIR process.

Microstructure controls and their effects on the properties of Bi2Sr2Ca1Cu2Ox superconductors

This paper reports our recent progresses in the development of Bi2Sr2Ca1Cu2O x /Ag tape conductors for the applications of magnetic field generation in liquid helium or around 20 K, using a refrigerator. We have carried out extensive work to optimize the processing parameters, investigating the relationship between the microstructure and transportJ c. We have found that the partial melting in oxygen atmosphere is effective to have large transportJ c with good reproducibility. The pre-annealing and intermediate rolling (PAIR) process has been successfully applied to the multilayer conductors to improve the grain alignment and transportJ c. TheJ c of 5×105A/cm2 at 4·2 K and 10 T has been achieved, which is the highest value reported so far. Two magnets fabricated by using different types of Bi-2212/Ag conductors were tested. One is a magnet designed as an insert magnet for a 18 T-class large bore Nb-Ti/Nb3Sn superconducting magnet. The conductor of this magnet was multifilamentary tape processed by powder-in-tube method. TheI c was 98 A in the backup field of 18 T, which generated the self field of 1·79 T. A large pancake coil was fabricated with multilayer conductor and tested under the operation of cryocooler system. The coil was stably operated up to theJ c of the coil at the temperatures below 30 K.

Improvement of J c and Grain Alignment of Bi-2212/Ag Multilayer Tapes by Pre-Annealing and Intermediate Rolling Process

The high transport critical current density (Jc) > 500 kA/cm2at 4.2 K, 10 T is obtained in the Bi-2212/Ag multilayer tapes fabricated by using PAIR (Pre-Annealing and Intermediate Rolling) and melt-solidification process. This Jcvalue is twice higher than existing high-quality Bi-2212/Ag tapes (250 kA/cm2). By applying PAIR process to Bi-2212/Ag tapes, Bi-2212 grain alignment is much improved and a large Jcenhancement is achieved. Jchas been increased strongly by performing pre-annealing at 840°C in oxygen (1 atm) and intermediate rolling with 25% deformation.

Spherulitic Growth of Poly(ethylene oxide) from Viscous Solution

Spherulitic growth of poly(ethylene oxide) from 30 wt% tripropionin (glycerol tri-n-propionate) solution was investigated in the supercooling range ΔT=11–37 K. The solution was pre-annealed at 200°C before isothermal crystallization. The estimated total crystallization rate decreases with increasing pre-annealing time, and becomes almost constant with a pre-annealing time longer than ca. 200 h. This suggests that traces of crystalline nucleus remaining in the solution dissolve during the pre-annealing process. The isothermal crystallization rate G with respect to the crystallization temperature was measured using isothermal calorimetric measurements and direct observation of the spherulitic growth using a CCD camera. The Avrami exponent estimated from the isothermal crystallization data ranges from ca. 2.7 to 3.2 depending on the crystallization temperature. The profile of G vs. T was also analyzed to estimate the parameters for the diffusion factor, and the result shows that the diffusion process belongs to the low friction limit, i.e., frictional interaction between the polymer and solvent is extremely weak.

Bi 2Sr 2CaCu 2O x/Ag multilayer tapes with Jc>500 000 A/cm 2 at 4.2 K and 10 T by using pre-annealing and intermediate rolling process

The high transport critical current density ( J c)>500 000 A/cm 2 at 4.2 K, 10 T (critical current>700 A) is obtained in the Bi-2212/Ag multilayer tape fabricated by using the PAIR ( Pre- Annealing and Intermediate Rolling) and melt–solidification process. The combination of the improvement in geometric configuration of the tape and PAIR process make it possible to obtain the most preferable microstructure and enormous J c. Effect of processing and geometry of the tape on J c and Bi-2212 grain alignment has been studied. The enormous transport J c is attributed to highly textured grain alignment and uniformity in the tapes, which are achieved by PAIR process. After post annealing in flowing argon at 450°C for 4 h, transition temperature T c is increased from 83 K to 92 K and transport J c>25 000 A/cm 2 at 77 K is obtained. PAIR process is applicable for fabricating long Bi-2212 tapes with large transport J c for practical applications.

Effects of PAIR (pre-annealing and intermediate rolling) process on superconducting properties of Bi 2Sr 2CaCu 2O x/Ag multilayer tapes

PAIR process, which is the combination of pre-annealing (PA) and intermediate rolling (IR) processes and is performed prior to melt-solidification, enhances J c of the Bi-2212/Ag composite tapes. The effects of pre-annealing and intermediate rolling process on microstructure and J c of the Bi-2212/Ag multilayer tapes fabricated by the oxide-painting method have been studied. The results show that J c has been increased strongly by performing pre-annealing at 800–880°C and intermediate rolling with >25% deformation. Transport J c of 3.3×10 5 A/cm 2 in magnetic field (4.2 K, 10 T) is obtained. The enhancement of J c is assigned to the microstructure with high grain alignment and uniformity, as well as the improvement of grain coupling by the PAIR process.

The effects of heating and annealing processes on the surface morphology and quality of double-sided YBa 2Cu 3O 7− δ thin films

A series of YBa 2Cu 3O 7− δ (YBCO) double-sided thin films were prepared by pulsed-laser deposition (PLD) and measured by XRD, SEM, AFM, electrical-transport and microwave surface resistance ( R s) measurements. The results showed that the surface morphology of the first side of the film consisted of more troughs and big particles, while that of the second side of the film consisted of almost no troughs but small, bar-like oriented particles. The difference has been attributed to the heating and annealing processes during deposition. The improved substrate surface conditions for the deposition of the second side of the film led to better film quality in terms of the T c0 and R s values. Our results implied that a pre-annealing process of the substrates and a proper post-annealing process of the films after deposition would improve the film quality and reduce the difference between the two sides of the YBCO films fabricated by PLD.

Fabrication of high current carrying Bi-2212/Ag superconducting tapes by the pre-annealing and cold rolling process

The pre-annealing and rolling process is employed to improve the microstructure and J c for Bi-2212/Ag tapes fabricated by using the dip-coating method and melt–solidification process. It is found that J c has been enhanced significantly in tapes processed by the combination of pre-annealing at 800–880°C and cold rolling at the deformation rate of 20–30%. The increase of J c is assigned to the enhancement of c-axis grain alignment and the uniformity of the Bi-2212 layer that brings about the improvement of grain coupling. This method is promising for fabricating long BSCCO tapes with homogeneous and high transport J c.