Search for New High-Tc Superconductors at Elevated Temperatures

One of the long-standing challenges in experimental superconductivity are the sustained efforts to achieve stable and cheap superconducting materials at room temperatures. There are still no guiding paths or theories, to fulfill this aspiration. It appears that most of the high-Tc superconducting materials reported in the last 3–4 decades were accidently discovered. Recently, high-temperature superconductors in various hydrogen-rich compositions have been reported. However, all these substances superconduct under extremely high pressures only, not achievable in most laboratories. In this review article, we summarize two unsuccessful methods used by us to achieve high-Tc superconductors under ambient pressure. We summarize our observations made on the basis of the conventional superconducting-magnetic phase diagrams and on the YFe₂X₂ (X = Si, Ge) systems in which Fe is not magnetic. On the other hand, superconducting phases up to 65 K were accidently discovered in commercial amorphous carbon (a-C) which contains traces of sulfur. The third part describes attempts to produce superconductivity in synthesized a-C powders and thin-film doped with sulfur (a-CS at ambient pressure. The a-CS materials have the same ingredients as the recent CH₄-H₂S-H₂ gases, which are superconducting at Tc = 289 K under high pressure of 267 GPa.