Formation and quantification of peroxide anions in nanocages of 12CaO•7Al2O3

The concentration of peroxide (O-2(2-)) ions in the cage structures of the mayenite (12CaO center dot 7Al(2)O(3) or C(12)A(7)) crystal lattice has been determined quantitatively by Raman spectroscopy combined with volumetry and electron paramagnetic spin resonance. The formation process of the O-2(2-) ion was also investigated using in situ Raman spectroscopy under controlled atmospheres. Although room temperature Raman spectroscopy showed that the equilibrium concentration of O-2(2-) ions in the cage structures increased with increased annealing temperatures (especially below 800 degrees C), no O-2(2-) signal was observed at very high temperatures (1350 degrees C) during the in situ measurements. We explain this apparent inconsistency by hypothesizing that transient atomic oxygen, possibly originating from the thermal dissociation of atmospheric O-2, is formed at interstitial or cage sites within C(12)A(7) at high temperatures and subsequently combines with O2- ions in the cages to form O-2(2-) during the cooling process.