Disorder of O2- ion and incorporation of O- and O2- radicals in nanoporous crystal 12CaO•7Al2O3 studied by low-temperature heat capacity measurements

Heat capacity of nanoporous crystal, 12CaO center dot 7Al(2)O(3) (C12A7), was measured between 8 5 mK and 5 K under magnetic field up to 9 T. The heat capacity under zero magnetic field did not fit to the T-3 law; the deviation was discussed in terms of the disorder of the O2- ions in the subnanometer-sized cages in C12A7 lattice. Under magnetic field, the heat capacity showed a Schottky-type anomaly due to the Zeeman splitting of O- and O-2(-) radicals (S = 1/2) incorporated in the cages. The total concentration of O- and 02 radicals in the crystal was estimated to be 4.4 x 10(18) cm(-3) (2.3 x 10(21) mol(-1), 3.8 x 10(-3) mol mol(-1)). (c) 2006 Elsevier B.V. All rights reserved.