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 al pha-forms of LiYO2:5% Eu3+ at 77 and 383 K, were refined utilizing neu tron diffraction data on a powder sample. DSC experiments on an anneal ed 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 fo r the penetration of water, hence the formation of an hydrated crust a t the surface of the grains. Theoretical crystal field parameters of E u3+ in C-1 and D-2d site symmetries are calculated utilizing the newly refined atomic coordinates. Experimental (empirical) crystal field pa rameters are fitted utilizing a 387 x387 interaction matrix. (C) 1998 Academic Press.