Single crystal growth of nanoporous C12A7:e- by controlling melt state

It has been known that electron doped 12CaO-7AI ₂0 ₃ (C12A7:e _-, electride) single crystals, which are composed of a closed-packed periodic quantum dot structure, may be prepared by strong reduction of the precursor C12A7:0 ^2-, but direct single crystal growth of the C12A7:e ^- from the melt state has never been achieved to date. We report the melt state of polycrystalline electride in pure dry Ar atmosphere at temperatures of 1290∼1500 °C, which leads to the direct single crystal growth of the C12A7:e ^- from the melt. The electride single crystals with a diameter of 7 mm and a length of 43 mm have been grown by a floating zone method, where a polycrystalline electride feed and an electride single crystal seed rod were employed. The electron concentration in the crystal increased up to ∼1.0 x 10 ²⁰ cm ^-3 as the growth proceeded. The present findings suggest that electron-entrapped local structure may exist in the melt and the electrons may act as a template for the formation of C12A7 electride in the solidification process of the C12A7 lattice.