SYNTHESIS AND SUPERCONDUCTIVITY OF OXYCARBONATES OF THE TL-1201 PHASE

TlBaxSr4-xCu2(CO3)Oy oxycarbonates with the Tl-1201 structure were synthesized over a wide range of x (1.0 less-than-or-equal-to x less-than-or-equal-to 3.2) and examined by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy and magnetometry methods. New phases with the Tl-1201 structure having 6 and 7 times periodicities along the b-axis were isolated. The former was stable for a wide Ba-rich range (1.8 less-than-or-equal-to x less-than-or-equal-to 3.2), and the latter was observed for a smaller Ba content range (1.2 less-than-or-equal-to x less-than-or-equal-to 1.6). The phase stability was found to depend on the synthesis condition. The maximum T(c) of the as-synthesized specimen in this series occurred at about 70 K around x = 2.0. The Meissner volume fraction of the as-synthesized specimen (x = 2.4) was 30% at 5 K.