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

It has been known that electron doped 12CaO x 7Al2O3 (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:O2-, 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 approximately 1500 degrees 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 approximately 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.