Solid State Syntheses of 12SrO·7Al₂O₃and Formation of High Density Oxygen Radical Anions, O⁻and O₂⁻

Abstract

A new synthetic route via a solid-state reaction, the crystal structure of 12SrO·7Al 2 O 3 (S 12 A 7 ) incorporated with OH − ions, and the formation of oxygen radical anions in S 12 A 7 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·7Al 2 O 3 (C 12 A 7, a mayenite structure) and demonstrate that two Sr 2+ ions (pole Sr 2+ 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 Sr 2+ ions rather than adsorbed on one side.