Rare earths in superconductors

Research activity in the field of superconductivity has been extensive and continues to be of interest globally. As a result of the discovery of the property of superconductivity, mercury was observed to conduct an electrical current without resistance. This observed state of zero resistance and perfect diamagnetism and the nature of magnetic flux penetration into superconducting materials have continued to draw the attention of materials scientists and solid state scientists. 

The compounds of the type YBa2Cu307 are broadly known as a family of 1,2,3-compounds. These are compounds consisting of multiple phases. It is also disturbing to note that the precise composition and constitution of these compounds and their role in exhibiting the properties are not completely clear. It also appears that the properties of the compound are independent of the rare earth present in the compound. Superconductivity has been observed at relatively high temperature in the case of all the rare earths in 1,2,3-compounds. One of the stringent requirements is that the starting materials from which the 1,2,3-compounds are synthesized have to be pure. 

A plot of Tc with time is shown in Fig. 12.26 to illustrate the developments. 

Superconductivity in the multiphase quaternary borocarbide system Y-Ni-B-C has been recently reported [141,142], Earlier work on valence fluctuations in ternary borides RENiaB were studied and in the case of YNi4B, a weak but reproducible signal of superconductivity at Tc of 12 K was observed. This is the first report or discovery of a ternary superconducting phase of the elements Y, Ni and B with a high Tc value (Fig. 12.27). 

MODERN ASPECTS OF RARE EARTHS AND THEIR COMPLEXES 

---