A new magnetic grain alignment technique has been applied to produce biaxially aligned YBCO coated tapes. A biaxially aligned dispersion of orthorhombic Y 2 Ba 4 Cu 7 O 15 (Y-247) powder was settled on untextured silver substrates. The Y-247 tapes were then melt processed to achieve high critical current YBa 2 Cu 3 O 7 (Y-123) tapes with CuO as a secondary phase. The biaxial alignment is preserved after the densification process and a clear enhancement of J c relative to identically prepared untextured or uniaxially textured samples is obtained. Critical current densities of up to 5000 A cm −2 at 77 K in self-field and 1500 A cm −2 in 0.5 T magnetic field at 65 K were obtained in films from 20 to 40 µm thick. Problems were experienced in achieving fully densified thick films while retaining biaxial texture. The initial grain size distribution was found to have a major influence on the final microstructure.Provided significant improvements in J c can be obtained this method offers an alternative to coated tape processes based on epitaxial growth which has the advantage that it does not require textured substrates. The biaxial alignment technique described here intrinsically acts on the bulk material rather than at surfaces. This offers the possibility of texturing without thickness limitations.

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We have measured the thermopower and resistivity of two series of cuprate superconductor, TI,.,Pb,,,Sr,_,La,CuO~ and Bi,Sr,-,LaxCuO,+, , which possess a single CuO, plane. In each series, the hole concentration can be varied by changing the La content, permitting investigation of the overdoped, maximum-T, and underdoped regimes. The thermopower follows a pattern similar to that seen in superconductor series with more than one CuO, plane, namely an approximately linear decrease as temperature increases well above T,. However, the thermopower shows a minimum above T, followed by a maximum as temperature increases for samples with a small thermopower and high T,. The magnitude of thermopower as a function of To is in general agreement with the universal behaviour found for other cuprate superconductors.

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