Solid State Syntheses of 12SrO•7Al2O3 and Formation of High Density Oxygen Radical Anions, O- and O2-

A new synthetic route via a solid-state reaction, the crystal Structure of 12SrO center dot 7Al(2)O(3) (S(12)A(7)) incorporated with OH- ions, and the formation of oxygen radical anions in S12A7 have been examined. Investigations using X-ray powder diffraction and thermogravimetric and evolved gas combined analyses demonstrate that homogenization promoted by molten Sr(OH)(2) hydrates and the presence of Sr-hydrogarnet precursors play crucial roles in the formation of S(12)A(7). Rietveld analyses confirm the lattice framework of S(12)A(7) has a structure identical to that of the nanoporous crystal 12CaO center dot 7Al(2)O(3) (C(12)A(7), a mayenite structure) and demonstrate that two Sr2+ ions (pole Sr2+ ions) on the S-4 axis of a cage displace toward the cage center owing to the accommodation of an OH- ion. An electron paramagnetic resonance study demonstrates that oxygen radical anions, O-2(-) and O-, are generated in the cages with concentrations on the order of 10(20) cm(-3) each by oxygen annealing. From the g-values observed at 77 K, the oxygen radical anions are interpreted as being sandwiched between the two pole Sr2+ ions rather than adsorbed on one side.