Melt-textured Growth Research Articles

Enhanced Jc in air-processed GdBa2Cu3O7−δ superconductor bulk grown by the additions of two Nd2BaCuO5 seeds

By using top seeding melt-textured growth process, single domain GdBa2Cu3O7−δ bulk superconductor has been fabricated successfully in growth with the additions of two Nd2BaCuO5 (Nd123) seeds. Both microstructure and superconducting properties were investigated from the seed position to the boundary of the sample. The experiments showed the enhanced superconducting properties such as the critical current density (Jc) and the irreversibility (Birr) in the edge of the domain and the part between two seeds. The additions of two Nd123 seeds accumulate the richer Gd2BaCuO5 inclusion particles and improve the Jc at the edge of single domain, which is confirmed by scanning electron microscopy.

Enhanced Growth Rate of a YBCO Bulk in the Melt-Textured Process Under 1 atm Oxygen Pressure

By the employment of 1 atm oxygen pressure as the growth atmosphere, we report a success in the enhanced growth rate of the melt-textured (MT) YBCO bulk. A well-oriented c -axis single-domain bulk with a size of 42 mm in diameter was fully grown at a high average growth rate of about 0.32 mm/h, which is 1.5 times larger than that in air. It was found that the increased oxygen partial pressure has a profound influence on the MT growth (MTG) for YBCO. The enhanced growth rate can be interpreted by both increased solubility and diffusion coefficient of yttrium in the Ba-Cu-O liquid under high oxygen partial pressure. After oxygenation, single-domain samples were determined to have a sharp superconducting transition temperature at 91.7 K, indicating that the superconductivity of crystals grown under high oxygen pressure does not degrade. Additionally, due to the rapid growth, the trapping effect of Y211 particles becomes predominant. As a result, a relatively more homogeneous distribution of Y211 particles was observed in the Y123 matrix. Finally, the most important advantage of this technique is that the enhanced growth rate of Y123 gives less opportunity from self-nucleation in the liquid, which takes place beyond the growth window and the embryonic period. Thus, this oxygen-increased MTG process is very promising for producing large-sized YBCO bulks with good superconducting properties.

MT growth visualized in an LLCPK1 cell expressing GFP-EB1 to mark the growing MT plus ends: Movie 32_2.

MT growth visualized in an LLCPK1 cell expressing GFP-EB1 to mark the growing MT plus ends: Movie 32_2.

Growth of a high performance SmBCO bulk superconductor with the addition of aSm2Ba4Cu2O9 phase

By adding a novel Ba-rich Sm2Ba4Cu2O9 (Sm242) compound in the precursor material high performanceSmBa2Cu3O7 (Sm123or SmBCO) bulk superconductors were successfully grown in air by melt-textured (MT) growth. Highly-c-orientedSmBCO and NdBa2Cu3O7 (Nd123 or NdBCO) thin films with a superheating property were effectively utilized as seeds toinduce an epitaxy nucleation and growth. A primary study on the effect of the Sm242 additionon superconducting properties was carried out, proving that the critical transition temperature(Tc) can be substantially improved. It was found that, with the addition of 10 mol% Sm242, a highTc of over 94 K with asharp transition (ΔTc less than 1 K) can be achieved in the air-processed Sm123 bulk. A relatively strong peak effect in theJc–H curve is present at the intermediate field range, which might be attributed to the formationof a compositional fluctuation within the Sm123 matrix. An improvement in theparticle size and distribution of Sm211 in the Sm123 matrix was also observed.

A new seeding approach to the melt texture growth of a large YBCO single domain withdiameter above 53 mm

A new approach for growing large size single domains of Y–Ba–Cu–O by a top-seededmelt-textured growth (TSMTG) process is reported. Contrary to the commonly used TSMTGmethod using a small seed crystal that has been difficult to use to grow well-textured singledomains with diameters above 50 mm, we adopt a large well-textured SmBCO bulk with a size of14 × 14 mm2 as a seed to grow YBCO single domains. Experimental results show that this new approachcan not only quicken the growth rate of the bulk, but also result in a better texturedstructure. By using this method, large YBCO single domains of up to 53 mm indiameter have been successfully produced and 75 mm diameter samples can also begrown. Microstructure analysis of these as-grown YBCO bulks shows a goodc-axis orientation in crystallization, and magnetic levitation force measurements show thatthe bulks 53 mm in diameter have excellent magnetic levitation performance, withlevitation force of up to 334 N (77 K, 0.5 T), corresponding to a force density of 15.2 N cm−2.

Growth and investigation of SmBCO/Ag single grain bulk for batch production of Sm123 seed crystals

Using NdBa 2Cu 3O y (Nd123) bulk material as a seed, we report a success in the melt-textured growth of SmBCO/Ag bulks by cold-seeding melt-growth process. Very well-textured single domain bulks of SmBCO with 5 wt% Ag 2O addition can be fabricated reproducibly under ambient atmosphere. Microstructure analysis of the obtained SmBCO/Ag bulk sample reveals that no silver particle is trapped within the mono-domain region, where the peritectic decomposition temperature goes back to the one of the Ag-free SmBCO sample. This c-axis oriented mono-domain region can be easily separated into a large amount of Sm123 seeds. Therefore, a new approach to preparation of Sm123 seed crystals in high quantity and quality can be achieved in an uncomplicated way, which exhibits significant advantage in comparison with the conventional method for Sm123 seed fabrication by MgO cold-seeding process. Experimental results show that a batch of well-textured YBCO bulks has been grown successfully by using these new Sm123 seed crystals.

Vortex pinning properties of [formula omitted]–Ba–Cu–O and [formula omitted]–Ba–Cu–O superconducting bulks

We have studied the effect of a small amount of Y-site substitution by La or Pr ions on the vortex pinning in the Y–Ba–Cu–O system. ( Y 1 - x La x ) –Ba–Cu–O and ( Y 1 - x Pr x ) –Ba–Cu–O bulks were fabricated by the melt-textured growth, in which x was varied from 0 to 0.01. The critical current density J c at 77 K is improved in magnetic fields parallel to the c-axis above 2–4.5 T and the corresponding irreversibility field, H irr , shifts to the higher value in both bulks.

Melt-textured growth of (LRE)–Ba–Cu–O by a cold-seeding method usingSmBa2Cu3Oy thin film as a seed

A cold-seeding method for fabricating LRE-based (LRE: a light rare-earthelement) bulk superconductors under a reduced oxygen atmosphere is reported.We used Sm123/MgO thin films as seed crystals, and succeeded in growingc-axis oriented singlegrains for both LRE = Gd and LRE = Sm. Although a slight contamination of Mg from the seed crystal was detected,high quality bulk superconductors with diameters of 30 mm were successfullyfabricated under low oxygen partial pressure. In particular, the trapped field ofthe Sm-based bulk superconductor was 1.52 T at liquid nitrogen temperature.

Impact of the Starting Powder Composition on ${\rm GdSr}_{2}{\rm RuCu}_{2}{\rm O}_{8}$ Melt-Textured Processes

The superposition of strongly anisotropic magnetic and superconducting properties in GdSr2RuCu2O8 (Gd1212) stimulates interest in the fabrication of oriented samples of macroscopic size by Melt-Texturing Growth (MTG). Up to now, the results obtained are unsatisfactory due to the small size and the random distribution of the oriented domains. In order to achieve MTG samples with higher oriented volume fractions, we prepared pellets adding either GdSr2RuO6 (Gd1210) or CuO to highly pure Gd1212 powders. X-ray Diffraction (XRD) analysis revealed a substantial difference between the two systems showing that only in Gd1212-Gd1210 samples it is possible to achieve a superconducting phase. The analysis of the two samples microstructures carried out by Scanning Electron Microscopy with implemented Energy Dispersive Spectroscopy (EDS) revealed that in the case of the Gd1212-Gd1210 samples a low concentration of Gd1210 and SrRuO3 inclusions is observed in a Gd1212 predominant matrix. However, in the Gd1212-CuO samples, micro-sized precipitates of SrRuO3, islands of Gd2CuO4 are homogeneously distributed throughout a CuO matrix. DTA measurements performed on all the samples confirm the presence of additional solidification reactions in the Gd1212-CuO samples. These features have a profound impact on the transport properties of the two samples. The addition of Gd1210 in highly pure Gd1212 powders has been proved to be a favorable condition to obtain superconducting Gd1212 MTG samples.

Particle distribution in melt-processed Y 1.5 Ba 2Cu 3O x superconductors with BaCeO 3 addition

To understand the effect of BaCeO 3 on a Y 2BaCuO 5 (Y211) distribution, Y 1.5Ba 2Cu 3O x (Y1.5) superconductors with/without 1 wt.% BaCeO 3 additions were prepared by a top-seeded melt-textured growth (TSMG) process. Two different BaCeO 3 powders (as-synthesized (coarse powder) and an attrition-milled (fine powder)) were used and the size effect was compared with that obtained from a Y1.5 sample with no addition. A refinement of the Y211 particles was achieved for both the as-synthesized and attrition-milled BaCeO 3 additions. The distribution of the Y211 particles was most uniform in the Y1.5 sample prepared with the attrition-milled BaCeO 3 powder due to the reduced size of the Y211-free regions by the fine size BaCeO 3 addition. The highest J c was achieved in the Y1.5 sample prepared with the attrition-milled BaCeO 3 powder. The J c result agreed well with the microstructure variations by the addition of BaCeO 3 powders.

Studies on structural and magnetic properties of melt textured growth YBa2Cu3O7-x superconducting bulk materials

In this study, production methods and the structural and magnetic properties of melt-textured growth of YBa2Cu3O7-x bulk superconductors are discussed. During the research; various temperatures for melt texturing are tried for the optimization of the production of bulk YBCO. With the help of AC magnetic susceptibility measurements, some insights for the produced samples are handed out including critical phase transition temperatures and the effects of crystal growth inside the YBCO samples. XRD measurements showed bigger and greater number of crystal growth in a correlation with the increasing temperature and the microphotographs of the samples verified successive growth of YBCO crystals inside the samples. Sharper phase transition is reached with the increasing texturing temperature. Top seeding for the selected crystal orientation has also been tried at the 1070oC for the texturing temperature, but the resulting melt textured sample was not different with the only-textured sample in the means of magnetic properties. Optimization over the texturing temperature found out to be between 1070oC and 1080oC while this result only depends on magnetic and structural properties.

Melt-Textured Growth of Grain Aligned Bulk Oxide Thermoelectrics

AbstractA new process, based on melt processing has been investigated with oxide thermoelectrics to achieve long-range grain alignment for low resistivity as well as to embed secondary phase precipitates and associated crystal defects for low thermal conductivity. Melt-processing of Bi2Sr2Co2Ox and CaMnO3 has been studied. A high degree of (00l) grain alignment has been achieved by melt processing. Good values of Seebeck coefficient of nearly -250 μV/K were measured in the melt-processed CaMnO3. Secondary phases of Ca4Mn3O10 and CaMn2O4 are found to be trapped between the aligned grains which led to high electrical resistivity values and limited the figure of merit in our initial samples.

Effect of Pr doping on the growth and superconducting properties of(Y1−xPrx)Ba2Cu3O7−δ

(Y1−xPrx)Ba2Cu3O7−δ (Pr-YBCO, x<0.2) single crystals and single domain bulks were grown by the top-seededsolution-growth (TSSG) and the top-seeding melt-textured growth(TSMTG) methods, respectively. The superconducting critical temperature(Tc) was determined by magnetic measurements and the critical current density(Jc) was estimated by applying the modified Bean model. For a low-level substitution(x<0.025), an increasein the Jc value as compared with that for unsubstituted YBCO was found while no apparent change in theTc value was noticed. On the other hand, Pr substitution in YBCO leads to: (i) increasing liquid solubilityof the total rare earth element in the Ba–Cu–O solution, (ii) increasing peritectic temperature(Tp), and (iii) a decrease in the liquidus slope near theTp. As a result, the driving force for YBCO growth and the region of singlegrain growth are enhanced. Study of the compositional correlation betweenliquid and solid additionally indicates that the Pr distribution coefficient islarger than 1 in the Pr-YBCO system. Thus the Pr content and then theTp value of Pr-YBCO in the bulk reduce with the growth time during TSMTG. The lowerTp valuein the final crystallized part is beneficial to a slow cooling process. Using the TSMTG method, Pr-YBCO(x = 0.02) monodomains up to 42 mm in diameter were grown with a high growth rate.

Anisotropic thermal conductivity of Er–Ba–Cu–O bulk superconductors

We have measured the temperature dependences of the thermal conductivity in the ab-plane, κ ab ( T), and along the c-axis, κ c ( T), respectively, for the Er–Ba–Cu–O bulk superconductors, which were fabricated by a method of the melt texture growth. Above the critical temperature T c, the κ ab decreases quite moderately as increasing temperature or is almost independent of the temperature. Below the T c, the well-known enhancement is observed but is relatively small. The κ c ( T) shows the small absolute values and we found that the anisotropy of the thermal conductivity ( κ ab / κ c ) for Er–Ba–Cu–O bulks is of about 2–6.

Remarkable peak effect in Jc( H, T) of Y–Ba–Cu–O bulk by using infiltration growth (IG) method

This study presented the superior superconductivity of Y–Ba–Cu–O (YBCO) bulk materials grown by using modified infiltration growth (IG) method with a small Sm–Ba–Cu–O crystal as seed. Compare to the bulks grown by melt-textured growth (MTG) method, IG bulk is denser and with finer second phase (Y 2Ba 1Cu 1O 5, Y211). In addition, remarkable peak effect was observed of the IG YBCO bulk material. Peak effect in J c( H, T) is an distinctive property of RE–Ba–Cu–O (RE = rare earth element, e.g. Sm, Nd) superconductors. However, it is found that peak effect is unusual in Y–Ba–Cu–O material. In this study, magnetism measurements also show peak effect in J c( H, T), especially at low temperatures. At 50 K, the peak position of J c( H, T) was about 5 Tesla. J c value of peak, J c(peak, 50 K), is comparable to that of self-field, J c(0, 50 K). On the other hand, it is noted that this effect is spatial-dependent, i.e. it only can be found in particular part of bulk. To interpret the mechanism of peak effect and the spatial-dependence, different microstructure analysis, which includes scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray absorption spectrum (XAS) were used. The results indicated that the composition is inhomogeneous throughout the bulk. Diffusion of Sm from seed to YBCO bulk was observed, which is believed to occur during high temperature, and thus changed the superconductivity. The inhomogeneity of microstructure was correlated to the spatial-dependent of peak effect. Finally, this study also demonstrates a possible way to introduce peak effect in YBCO materials and thus enhance the applications in high field regions.

Effects of Y 2BaCuO 5 content and the initial temperature of slow-cooling on the growth of YBCO bulk

In order to grow large mono-domain YBa 2Cu 3O 7− δ bulk in the tubular furnace, the effect of Y 2BaCuO 5 (Y211) content and initial temperature of the slow-cooling process on the growth of YBa 2Cu 3O 7− δ (Y123) bulk has been investigated. Single grain Y123 bulk samples with 20 mol% and 30 mol% Y211 addition have higher original crystallization temperature than that with 40 mol% Y211; however, the melt-textured growth rate of the single domain seems to be faster for the system with higher Y211 concentrations. In addition, it seems that the crystal growth of YBCO is extremely sensitive to the initial temperature of slow-cooling. The optimal initial temperature of slow-cooling process, which should be chosen according to the Y211 phase content, has been brought to the fore in the growth of large grain bulk. The above data is very useful for the fabrication of large grain (RE)–Ba–Cu–O bulk, and a group of YBCO single domain samples with diameter of 53 mm have been successfully produced, all of which present excellent magnetic levitation performance in the axial direction.

Observations of the influence of Y-211 inclusions on melt textured growth of single domainY–Ba–Cu–O

Single domain Y–Ba–Cu–O (YBCO) samples composed of aYBa2Cu3O7−δ (Y-123)matrix with Y2BaCuO5 (Y-211) inclusions were fabricated using the top-seed melt-textured growth (TSMTG)process. The influence of the Y-211 inclusions on the melt-textured growth mode has beenstudied for precursor pellets with a Y-123:Y-211 molar ratio of 1:0.2, 1:0.3 and 1:0.4.The surface morphologies obtained from these sintering pellets quenched from1000 °C,997 °C and 994 °C, respectively, have revealed that the initial peritectic recombination process near the seedcrystal seems to take place earlier for the Y-123 matrix with low Y-211 inclusions than forthat with a high level of Y-211 inclusions; however, the melt-textured growth rate of thesingle domain seems to be faster in the system with a high level of Y-211 inclusion than inthat with a low level.

Nano-Scale Pinning Centers in ${\rm Y}_{2}{\rm Ba}_{1}{\rm Cu}_{1}{\rm O}_{5}$ Doped Sm-Ba-Cu-O Superconductor

It has been suggested that the addition of nano-scale RE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> BaCuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (nmRE211, RE = Y, Sm and Nd) in melt-textured growth (MTG) Sm-Ba-Cu-O (SmBCO) materials enhances the critical current density (Jc), especially in high magnetic fields. According to the analysis of pinning properties, the field-induced pinning was attributed to a weakly superconducting phase. This phase was correlated to nano-scale compositional fluctuation regions originated from the peritectic reaction between nano-scale additives and matrix during the melt-growth process. To further elucidate the characteristics of the compositional fluctuation regions, in this study, nano-structure of nmY211 SmBCO samples were investigated using transmission electron microscopy (TEM) and electron energy loss spectra (EELS). Periodic nano-structures with width ranging from few to several tens of nanometers were observed throughout the matrix. Variations in both chemical composition and thickness of these periodic nano-structures were compared with the observations reported in the NEG ((Nd, Eu, Gd)-Ba-Cu-O) samples.

Thermal characterization of GdSr2RuCu2Oy-based mixtures in the GdSr2RuO6–CuO pseudobinary system

Fundamental to investigating the coexistence of superconductivity and magnetic ordering in GdSr2RuCu2Oy(Gd1212) is the fabrication of macroscopic crystallographically oriented samples. To achieve this, we need to identify the conditions in which Gd1212 incongruent melting reaction, producing solid GdSr2RuO6(Gd1210) in Cu-rich liquid, dominates over decomposition due to RuO2sublimation. Only in these conditions is it possible, indeed, to grow oriented samples by any melting and resolidifying technique. Moreover, the optimal mixture of Gd1212 and its melting products has to be identified to perform melt-textured or flux-flow growth. By means of thermogravimetric and differential thermal analysis (TG–DTA) we analyzed, up to 1200 °C in air, several mixtures of Gd1212 with Gd1210 or CuO, performing a scan of the entire CuO–Gd1212–Gd1210 coexistence line of the Gd–Sr–Ru–Cu–O phase diagram. Gd1212 melting temperatures have shown a certain dependence on composition, decreasing about 30 °C for high Gd1210 content samples and about 20 °C for high CuO content samples with respect to pure Gd1212. A huge undercooling was observed for resolidification processes that were revealed to start at temperatures around 990 °C. Measurements proved that in this range of temperatures in air, no mass is lost at the end of each melting process, so that they are not affected by RuO2sublimation. A strong dependence on the atmosphere has also been observed for pure Gd1212, melting temperature decreasing by more than 80 °C from 100% O2atmosphere to He atmosphere (less than 10−2% O2). Measurements revealed that high O2partial pressures favor RuO2sublimation, whereas low oxygen atmospheres prevent resolidification.

Melt-textured growth of NdBCO bulk seeded by superheating NdBCO thin film

In previous work, we reported that a superheating YBCO thin film was used to act as a seed for YBCO bulk growth by the melt-texture (MT) process. In this paper, we display a further development of using the NdBCO thin films as a homo-seed in the growing of NdBCO bulks with well c-axis orientation. Since in this process the NdBCO film endured a temperature as high as 1090 °C (for 1.5 h), which is higher than the T p of any REBCO compound, this success indicates that the NdBCO film could be a promising seed for epitaxially growing any RE–Ba–Cu–O bulks. According to the results of X-ray diffraction (XRD), we also found that the existence of extra phases in NdBCO film will lower the superheating property and consequently weaken its capability of being a seed.