Synthesis and properties of 12CaO · 7Al2O3 electride: review of single crystal and thin film growth

Abstract

Over the last decade, experimental studies supported by theoretical calculations have demonstrated that 12CaO · 7Al2O3 (C12A7), a typical electrical insulator, could be converted into an electro-active functional material, such as a metallic conductor with a low work function but chemical inertness and superconductivity, at low temperatures. These properties were realised by successful heavy electron doping into positively charged sub-nanometre-sized cages inherent to the crystal structure through removal of oxygen ions accommodated in the cages. The resulting samples, C12A7:e−, may be regarded as an electride in which electrons serve as anions. This article reviews the single crystal and thin film growth of both C12A7 and C12A7:e−, and describes our approach to these subjects on the basis of understanding the phase diagram of C12A7 and C12A7:e− as well as their molten and glassy states. Finally, the importance of the surface of C12A7:e− is addressed with regard to practical applications.