Composition simple and environmental friendly high temperature cuprate superconductors: Cu12(<italic>n</italic>−1)<italic>n</italic>

Abstract

High temperature cuprate superconductors are the only materials that have a T c higher than liquid nitrogen temperature at ambient condition so far. The comprehensive study of cuprate superconductors was selected as one of the 125 unsolved most challenging scientific issues published on Science . It triggers huge innovative scientific inquiry as well as of important application prospects. Heavy metal elements such as Rare-Earth, Bi, Tl and Hg etc are usually induced to stabilize the basic cystal structure in synthesis of the cuprate superconductors, which are classified as Y based system, Bi based sytem, Tl based system, respectively. As these heavy metal elements are usually expensive, volatile, or toxic, to develop new superconducting materials with simple and environmental friendly compositions but with T c above liquid nitrogen temperature, is a great challenge in superconductor material research. In this paper, we primarily focus on the author’s research to briefly introduce the Cu12( n −1) n (i. e., Cu homologous series) cuprate superconductors that are synthesized using high pressure method. The “Cu homologous series” superconductors comprise only copper and alkaline oxides, which are the simplest reagents that are necessary to form high T c cuprates as well as envioramental friendly compositions. The compounds can be synthesized only at high pressure high temperature and can be very stable at ambient pressure like artificial diamond. The properties measured in this paper are all measured at ambient pressure. “Cu homologous series” superconductors own a special crystal structure of a perovskite type charge reservoir layer, which presents a strong interlayer coupling, and exhibit excellent superconductivity properties at high temperature region. The advantages of the “Cu homologous series” superconductors include: (1) high T c above 120 K at ambient pressure, near Hg1223 that has the highest T c in cuprates; (2) excellent critical current densities at liquid nitrogen temperature, which are superior to Bi cuprate homologous superconductors and are comparable to the classical Y123 based system that are the best in terms of comprehensive properties; (3) containing alkaline earth copper oxides only but stable in air condition.