Refinement of the monoclinic and tetragonal structures of Eu3+-doped LiYO2 by neutron diffraction at 77 and 383 K differential scanning calorimetry, and crystal field analysis

The atomic coordinates and the temperature factors of the beta- and alpha-forms of LiYO2:5% Eu3+ at 77 and 383 K, were refined utilizing neutron diffraction data on a powder sample. DSC experiments on an annealed sample show that the monoclinic --> tetragonal transition occurs at 69 degrees C during the heating cycle and the reverse at 67 degrees C while cooling. Wide corridors lined by two parallel and adjacent Li-O rows running along the [100] and [010] tetragonal directions allow for the penetration of water, hence the formation of an hydrated crust at the surface of the grains. Theoretical crystal field parameters of Eu3+ in C-1 and D-2d site symmetries are calculated utilizing the newly refined atomic coordinates. Experimental (empirical) crystal field parameters are fitted utilizing a 387 x387 interaction matrix. (C) 1998 Academic Press.