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 · 7Al2O3 (C12A7), was measured between 85 mK and 5 K under magnetic field up to 9 T. The heat capacity under zero magnetic field did not fit to the T3 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 O2- radicals (S = 1/2) incorporated in the cages. The total concentration of O− and O2- radicals in the crystal was estimated to be 4.4 × 1018 cm−3 (2.3 × 1021 mol−1, 3.8 × 10−3 mol mol−1).