High temperature superconductors substitutions

It is found that the compound (Yo.6Cao.4)(SrBa)(Cu2.5Bo.5)07.8 with the ratio of Cu and B atoms equal to 5 1 is a high-temperature superconductor [28]. In principal, the crystal structure of this compound is isomorphic to that of YBa2Cu307 6. It would be interesting to make clear how B atoms substitute for Cu atoms in the crystal. 

Until 1988, all the high temperature superconductors that had been found were p-type, and it was assumed by many that this would be a feature of high temperature superconductors. However, some n-type superconductors have also been discovered, where the charge carriers are electrons the first to be found was based on the compound Nd2Cu04 with small amounts of the three-valent neodymium substituted by four-valent cerium—Nd2-/le/lu04-j where v 0.17 (samarium, europium, or praeseodymium can... 

HTSC high-temperature superconductor SLC substituted lanthanum cuprate... 

The high-temperature superconductors based on copper oxides have a principally perovskite structure. The crystal structures of four typical perovskite superconductors, BaPbA Bii- 3 (BPB), La (214), Y (123), and T1 (1223) are shown in Fig. 2. BPB is a simple perovskite, and the others are layered per-ovskites. The perovskite superconductors are classified in Table 1 from the viewpoint of crystal structure and constituent elements. Class 1 is the simple cubic perovskite with ABO-i composition. Typical of class I, BaPbArBii- Os was first synthesized by Sleight et al. in 1975 [9]. The parent compound is BaBiOa, whose Bi3+ site is partially substituted by Pb +. After the discovery of the high-temperature superconductors, it was found that the replacement of Ba by K also gives rise to a superconductor, Bai- cKjcBi03, with Tc = 28 K [10]. 

Positron annihilation is widely applied to study high-rc superconductors. After presenting the basic concepts (sect. 2) and discussing some experimental aspects (sect. 3), there is an overview of the results obtained so far in YBa2Cu307 (sect. 4), in YBa2Cu30y 5 with substitutions (sect. 5), and in other high-temperature superconducting oxides (sect. 6). 

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