Thallium barium calcium copper oxide

Thallium barium calcium copper oxide, or TBCCO (pronounced "tibco"), is a family of high-temperature superconductors having the generalized chemical formula Tl_mBa₂Ca_n−1Cu_nO_2n+m+2.

Schematic layered structure of TBCCO-2223.

Tl₂Ba₂Ca₂Cu₃O₁₀ (TBCCO-2223) was discovered in Prof. Allen M. Hermann's laboratory in the physics department of the University of Arkansas in October 1987 by the post-doctoral researcher Zhengzhi Sheng and Prof. Hermann.[1] The bulk superconductivity in this material was confirmed by observations of magnetic flux expulsion and flux trapping signals (under zero field cooled and field cooled conditions) with a SQUID magnetometer in the superconductor laboratory of Timir Datta in the University of South Carolina.[2] Allen Hermann announced his discovery and the critical temperature of 127 K, in Houston, Texas at the World Congress on Superconductivity organized by Paul Chu in February 1988.

The first series of the Tl-based superconductor containing one Tl–O layer has the general formula TlBa₂Ca_n-1Cu_nO_2n+3,[2] whereas the second series containing two Tl–O layers has a formula of Tl₂Ba₂Ca_n-1Cu_nO_2n+4 with n =1, 2 and 3. In the structure of Tl₂Ba₂CuO₆ (Tl-2201), there is one CuO₂ layer with the stacking sequence (Tl–O) (Tl–O) (Ba–O) (Cu–O) (Ba–O) (Tl–O) (Tl–O). In Tl₂Ba₂CaCu₂O₈ (Tl-2212), there are two Cu–O layers with a Ca layer in between. Similar to the Tl₂Ba₂CuO₆ structure, Tl–O layers are present outside the Ba–O layers. In Tl₂Ba₂Ca₂Cu₃O₁₀ (Tl-2223), there are three CuO2 layers enclosing Ca layers between each of these. In Tl-based superconductors, T_c is found to increase with the increase in CuO₂ layers. However, the value of T_c decreases after four CuO₂ layers in TlBa₂Ca_n-1Cu_nO_2n+3, and in the Tl₂Ba₂Ca_n-1Cu_nO_2n+4 compound, it decreases after three CuO₂ layers.[3]