High-Temperature Superconducting Materials

Abstract

Since the discovery of superconductivity in 1911 by the Dutch physicist Kamerlingh Onnes, who first observed this phenomenon in mercury at 4.2 K (-269°C),^(l) as shown in Fig. 1, there has been a succession of materials that superconduct at increasingly higher temperatures. Tens of metallic elements and thousands of compounds are now known to exhibit this propety. Until the mid-1980s, the highest recorded superconducting transition temperature was about 23 K (-250°C), in niobium germanate (Nb₃Ge). In 1987, however, a new class of materials that superconduct at temperatures above the boiling point of liquid nitrogen (77 K) were discovered. These so-called HiTc materials, which are usually ceramic in nature (i.e., complex polycrystalline metal oxides), may prove to be of considerable technological importance since they offer great potential for a wide range of both novel and existing applications. Although the superconducting mechanism in HiTc compounds is not yet fully understood, their emergence has been heralded as potentially the most significant scientific event since the advent of the transistor.