Superconducting phases in a remarkable class of metallic ceramics

MAX phases are a large group of nanolaminated carbide and nitride materials of immense scientific and technological interest. Materials of this class are known as metallic ceramics as they show a remarkable combination of metallic (electrically and thermally conductive, damage tolerant, resistant to thermal shock, and readily machinable) and ceramic (lightweight, resistant to oxidation, and elastically rigid) properties at the same time. To date, about 80 MAX phases have been synthesized, and more than 650 MAX phases are predicted to be synthesized in the future. At present, there are nine MAX phase nanolaminates that show superconducting transitions at low temperatures. Although MAX phases have been studied extensively, thorough understanding of the correlation between electronic structure and physical properties is still somewhat limited. Here we review the physical properties of superconducting MAX phases on the basis of electronic structures using first-principles density functional theory.