Materials Science of Electrides


Electrides are materials in which electrons serve as anions. These materials may be regarded as the solid form solvated electrons and were first synthesized employing organic ethers as complexant in 1982. Since then, electrides have attracted attention as an exotic materials based on a novel concept.However, the fatal drawback of organic electride materials was very high sensitivity to heat and water/O2, which was the obstacle to unveil the intrinsic properties. We overcome this issue by synthesis of a stable electride in 2003 using an inorganic crystal with 3-dimensionally connected cage structure. Materials research on the stable electrides clarified these materials exhibits interesting properties such as insulator-metal transition, superconductivity and ferromagnetism. Among them, low work function is a common property of electrides, showing possibility of various applications in electronics and chemical reactions. Concept of electrides was extended with respect to several aspects: from ionic materials to intermetallics in host materials, from crystalline to amorphous solids, and 0-dimensional to 1 and 2 dimensional materials in electron-confined space. In particular, 2D-electride in which anionic electrons are sandwiched by cationic slabs, is a bulk form of 2-dimensional electron gas, exhibiting large electron mobility and attracting a platform of topological materials. Exploring new electrides by computational approach has rapidly advanced. As a result, it is now coming a consensus that an electride is a stable equilibrium phase of many elements and compounds under high pressure. I talk the recent progress in materials and application of electride.

Hideo Hosono
Tokyo Institute of Technology