STRUCTURE AND SUPERCONDUCTIVITY STUDIES ON LNBA2-XSRXCU3O7 (LN=YB AND LU - 0.0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5)

The title compounds have been synthesized and studied with a view to stabilize the 123 structure and achieve single phase formation. Single phase and high T(c) are obtained with Sr content as low as x = 0.1 in the case of Yb. The single phase region extends only up to x = 0.5, in contrast to the Sr substituted Y-123 system wherein the single phase region has been established up to x = 1.2. The T(c, zero) decreases systematically with increase in x. Preliminary results of thermopower on two of the single phase compounds (x = 0.1 and 0.2) show a negative thermopower at all temperatures above T(c) with temperature dependence similar to that of Y-123. In the case of Lu, Sr substitution does not completely stabilise the 123 phase for any x. However, the quantity of the 123 phase is increased significantly for x = 0.4-0.5 when compared to x = 0.0. Structural, electrical and magnetic data are discussed.