Ceramic high-Tc superconductors HTSs

Access to the Handbook of Superconducting Materials edited by D.A. Cardwell and D.S. Ginley [34] and the Handbook of Superconductivity edited by C.P. Poole Jr [35] is recommended. The review by R.J. Cava [36], focused on the structures of the high-Tc superconductors, should also be consulted. 

A significant step in the history of the HTSs was the discovery in 1966 of superconductivity in the oxygen-deficient perovskite SrTi03 5, containing some barium or calcium substituted for strontium. Although the Tc value was very low (0.55 K), in retrospect it can be seen as the first superconducting ceramic. In 1979 a Tc of approximately 13 K was discovered for BaPb075Bi025O3, which also has the perovskite structure. 

The breakthrough came in 1986 when J.G. Bednorz and K.A. Muller [37] reported superconductivity with Tc = 35 K in the semiconducting ceramic, 

This discovery stimulated what can only be described as frenzied research in many laboratories throughout the world which quickly resulted in the discovery of YBa2Cu307, the so-called T23 phase, or YBCO, with a transition at a temperature as high as 93 K. There are also bismuth-based high-Tc superconductors, which are described below. 

The structure of YBCO is closely related to that of perovskite as evident in Fig. 4.54, which shows the unit cell consisting of three perovskite-type cubes with Cu ions at the corners and O ions at the centres of the cube edges. The top and bottom cubes contain Ba and the centre cube Y. 

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