Atomic Hydrogen in the Mineral Brasilianite NaAl3(PO4)2(OH)4

Abstract

Abstract EPR parameters for atomic hydrogen in three nonequivalent special positions at the twofold axis of the monoclinic structure of brazilianite, formed by X-ray irradiation at room temperature, are reported. The g-factors are practically isotropic and close to the free electron value, but the hyperfine splittings exhibit considerable anisotropy. One of the centers shows an additional doublet splitting, most likely due to hyperfine interaction with the proton of one of the OH groups. These hydrogen atoms have the highest thermal stability yet reported. With repeated thermal destruction and formation by ionizing radiation one of the centers is rapidly depleted. Thus they must be formed at defect sites, not from the undisturbed OH groups, and trapped near the sites of formation and their thermal destruction must at least in part be irreversible. Possible defects for their formation are discussed.