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.

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.

Large domain YBa2 Cu3 07-δ/2BaCuO5 (YBCO) samples were prepared by top-seeded melt-textured process, with the addition of SnO2 and CeO2 or PtO2. It was found that, in comparison to that in the CeO2-doped sample, the YBa2 Cu3 O7-δ(123) matrix was twisted in the PtO2-doped sample and its Y2BaCuO5 (211) particles were larger on average and less homogeneously distributed. The PtO2-doped sample showed a more obvious second-peak effect, and higher values of a-b plane critical current density (3Jcab) and irreversibility fields (Bt,,). The enhancement of3 Jcab is related to the microstructure inhomogeneity and the core surface AK pinning.

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.