CO2 distribution in CO2–rich melanophlogite from Fortunillo, Tuscany, Italy

CO 2 distribution in M 12 and M 14 cages of CO 2 – rich melanophlogite from Fortunillo, was studied using synchrotron powder X – ray di ff raction. Original and two heat – treated samples at 500 and 1000 °C were studied at room temperature. The di ff raction patterns of these samples can be indexed as a cubic cell ( Pm (cid:1)3 n ). For the non – heated sample, CO 2 occupancy for M 14 cage is close to unity, whereas about 0.85 for M 12 cage. For the 500 °C – heated sample, the occupancies for M 14 and M 12 cages are reduced to 0.79 and 0.57, respectively. Present study showed that CO 2 has preference to M 14 cage, but substantial CO 2 occupies M 12 cage. The electron distributions obtained by MEM analysis clearly reveal orientationally ordered CO 2 distribution in M 12 and M 14 cages. Present result is also used to clarify a recently proposed interpretation for the splitting of CO 2 Raman vibrational peak for the heat – treated melanophlogite.