Electron magnetic resonance in lithium oxide from a centre containing Fe3+

EPR has been performed on single crystals of nominally pure 7Li2O: (a) as grown, (b) after x-irradiation, and (c) after subsequent annealing. (a) shows evidence of several sites of Fe3+ in low abundance; (b) shows additional spectra from an electron centre with g = 2.003(1), associated with a brown coloration of the crystal, and also from Fe3+ at tetragonal sites; (c) shows that the electron centre (and the coloration) has been destroyed and the tetragonal Fe3+ concentration has been greatly enhanced. The fine structure parameters of the tetragonal Fe3+ centres, bo2= -0.1445(5) cm-1, bo4 = -27(3)x10-4 cm-1 and b44 = -90(2)x10-4 cm-1, are shown to be well described by the Newman superposition model, using a structural model for the centre comprising Fe3+ substituting for Li+ and two adjacent Li+ vacancies. Models are proposed for the changes that occur in this material on x-irradiation and annealing. (author)