Sol-gel is one of the effective techniques for preparing YBa2Cu3O7−δ (YBCO) coatings at relatively low cost. Its process from gel to oxide coatings, however, was not yet fully understood. This is one of the obstacles for achieving YBCO coatings with good superconducting properties. In this paper, we chose EDTA as the complexant to prepare gels with different kinds of M(EDTA)n−complexes, where M is any combination of Y, Ba, and Cu cations, in order to investigate the decomposition process of the gels with the help of Fourier transform infrared (FTIR) spectra. Comparing the FTIR spectra of the gel powders with those of the calcined powders, we found that the decomposed temperatures were different for different M(EDTA)n−complexes.We considered this was the cause of the Ba segregation (as BaCO3) in the coatings at low heating temperature, which in turn blocked the formation of high quality YBa2Cu3O7−δ.

Ultrafine SnO2 powder was made with grain size down to 20 nm. Such powder was introduced into the textured growth of Y1qx Ba2 Cu3 O7qd YBCO.superconductors. Crystalline inclusions, which were cubic in shape and from micrometer to submicrometer in size, were found trapped inside such grown YBCO superconductors. Determined by energy dispersive spectroscopy EDS., and further confirmed by X-ray diffraction, the composition of the inclusions was Y2Ba5 Sn3 yyyz Cuy Ptz.Ox. This Sn-based phase belongs to double perovskite structures. They were not trapped uniformly inside the YBa2Cu3O7yd 123., possibly caused by the agglomeration of the SnO2 powder at the very beginning. Nevertheless, it is possible for fine Sn-based inclusions down to a few hundred nanometers to be trapped inside the 123. The addition of the ultrafine SnO2 to YBCO textured superconductors without Pt did not seem to affect the size of Y2Ba Cu O5 211.particles. For comparison, Y2Sn2O7was also introduced to YBCO textured superconductor. In this case, the so-called f phase YBa3 Sn2 yx Cux O9yd was found. q1999 Elsevier Science B.V. All rights reserved.

Received 10 November 2000; received in revised form 24 January 2001; accepted 27 February 2001 By using top seeding melt-textured growth (TSMTG) process, large single domain YBaz Cu3 07 JY2 Ba Cu O5 (YBCO) samples were prepared with addition of nanometric SnO2 and normal CeOy. Polarized light microscope studies at each step of the TSMTG process showed that before YBa2 Cu3 07 δ (123) melting, the Sn-based reacted products were uniformly distributed in micrometer scale; after solidification, the trapped YyBaCuO5 (211) and Sn-based inclusions were more homogeneously distributed and with mean sizes of about one micrometer. Composition images of scanning electronic microscope for the textured samples showed that, on the whole, the Sn-based inclusions were smaller than the 211. They must be on average below one micrometer in size. Although evidence was found that very fine Sn-based inclusions were uniformly trapped in 123 matrix, the fraction of them was small in comparison to that of 211. No significant enhancement of superconducting critical current density (Jc) was evidenced for the nanometric SnOy-doped samples at a low magnetic field (B<1 T). However, values of Jc were decreased at intermediate magnetic field (1<B<3 T). 2001 Elsevier Science B.V. All rights reserved.

Weprepared precursors with fine BaZrO3 inclusions for melt-texture growth of high-temperature superconductors with nominal composition of Y1.5Ba2 Cu3 Oy-x BaZrO3 (x＝0, 0.04, 0.08, and 0.1), by the process of liquid-phase powder melt-texture growth (LPMG). We then investigated the effects of the precursors on the texture growth and the microstructure of composite YBa2Cu3O7-/Y2BaCuO5 (YBCO). The BaZrO3 particles were about 100 nm in size in the textured YBa2 Cu3 O7-(Y123), observed by the scanning electron microscopy (SEM). Owing to the pushing effects of growing fronts, fine particles were pushed out of and thus gathered in front of the growing fronts or between Y123 grains. The gathered particles in turn blocked the further growth of the Y123 grains. However, BaZrO3 particles seeded Y123 grains, giving rise to multigrain growths. These negative effects of BaZrO3 fine particles exclude themselves as effective flux pinning centers in the textured YBCO.

The Ca-doped YBa2Cu3O7−δ/Y2BaCuO5 bulk-textured superconductors were prepared by using the top-seeding melt-textured growth process. Composition analyses were made for such prepared samples. We found that Ca concentration in the YBa2Cu3O7−δ grains decreased along the growing direction; Ca preferred to substitute Y in the YBa2Cu3O7−δ grains, rather than to stay at the grain boundary. The accumulation of extra CuO at the growth front was considered as one of the causes of the inhomogeneous distribution of Ca.

The transverse Peltier effect is investigated on the top-seeded melt texture superconductor YBa2 Cu3 O7-δ (YBCO). By restricting the heat absorbing or evolving on one of the sample's surfaces, the Peltier heat flow is converted into a temperature difference for measurement. The temperature difference is found proportional to the current applied, which is in accordance with the prediction of transverse Peltier effect. Based on a simplified model, the difference of the Seebeck coefficients between the ab plane and the c axis, uSab2Scu, is about 35mV/K. It is in good agreement with that of large single crystal @I. Terasaki, Y. Sato, S. Tajima, S. Miyamoto, and S. Tanaka, Physica C 235-240, 1413～1994!#. The transverse Peltier effect is verified. This supports the idea that the off-diagonal thermoelectric effect is responsible for the anomalously high laser-induced transient transverse voltage on the oriented YBCO superconducting thin films.

Both the off-diagonal Seebeck effect and the off-diagonal Peltier effect were investigated on the same textured sample YBa2 Cu3 O7-s, and with the use of the same experimental setup. The effectiveness of several kinds of heat-conductive media was studied for the measurement. The flatness of both the sample and the heat-conducting block, and the matching between them were found very important for the reduction of the heat resistance of the interfaces. A reasonable agreement was found between the off-diagonal Seebeck coefficient measured by the off-diagonal Seebeck effect and that by the off-diagonal Peltier effect. The steplike feature in the relation between the off-diagonal Seebeck coefficient and the annealing temperature may imply a nonmonotonous change of the Seebeck coefficient along the c axis (Sc) with oxygen content.

It is reported that Ca-doping can improve the weak links between grain boundaries and increase the critical current density Jc of YBa2 Cu3 O7d polycrystalline films [Phys. Rev. B 58 (1998) 9543; Nature 407 (2000) 162]. In this paper, we investigated the preparation and superconducting properties of YBa2Cu3O7 d (YBCO) and Y1x Cax Ba2 Cu3 O7d (x=0.05, 0.1, and 0.2) (YCBCO) coatings on yttrium stabilized zirconia (YSZ) single crystal substrates by powder melting growth process. The X-ray diffraction (XRD) indicated that: (1) the coatings were of YBa2 Cu3 O7 d (Y123) phase with c-rientation; (2) the Y2 Ba Cu O5 (Y211) phase remained clearly in the YBCO coating, but much less in the YCBCO coatings. The effect of Ca-doping on the formation of the Y211 phase was analyzed with the help of the differential thermal analysis (DTA). The results of R-T and I-V relationship at 77K demonstrated that the zero resistance temperature Tc0 decreased with the Ca content, while the critical current density Jc (77K) was improved for x=0.05.

Both of the off-diagonal Seebeck effect and the off-diagonal Peltier effect were investigated with the use of the same textured sample YBa2 Cu3 07-δ (Y-123) and the same experimental setup. The reliability of the measurement is studied by applying different heat-conductive mediums. The flatness of both of the sample and the heat-conducting block, and the matching between them are found very important for the reduction of the heat resistance. The annealing effect on the S is also studied and found in accordance with that studied by the thermoelectric power.

idth at half-height of powder X-ray diffraction, the MgO powder was about 20nm in size on average. A supersonic vibration was introduced to destroy the accumulation of the ultrafme powder and to mix the powder with the YBa2 Cu3 07-δ precursor. The melt-process was employed to grow textured samples. From the Scanning Electron Microscope (SEM) graphs, some particles were found in the textured samples, which were about several nanometer in size. The composition of these particles, however, leaves to be identified. The magnetic critical current density (Jcm) at 77K dropped rapidly with the increase of Mg content.