Preparative and structural studies on the superconducting phase Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10/

Previously others have reported the existence in the system Tl-Ca-Ba-Cu-O of two high T/sub c/ (above 100K) superconducting phases, namely Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10+d/ (2223) and Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8+d/ (2122). They did not get samples pure enough for detailed analysis of crystal structure. The authors have just finished determining the crystal structure of the superconducting phase Bi/sub 4/Ca/sub 2/Sr/sub 4/Cu/sub 4/O/sub 20-x/. This bismuth-containing phase displays onset temperatures and T/sub c/ at 113 and 80K respectively. However, the thallium-containing phase of a similar metal-ion stoichiometry, namely, 2122 has a higher T/sub c/. They have prepared a homogeneous sample for the phase and determined its crystal structure by powder XRD method. Then the structural features of the present phase is compared with that of the bismuth-containing phase 4244. No occupancy problem for oxygen and cupric state of copper have been found.