INSTRUMENTAL NEUTRON-ACTIVATION AND ABSORPTION-SPECTROSCOPY OF PHOTOREFRACTIVE STRONTIUM-BARIUM NIOBATE SINGLE-CRYSTALS DOPED WITH CERIUM

Instrumental neutron activation analysis (INAA) was applied to determi ne the compositions of SrxBa1-xNb2O6:Ce single crystals with x = 0.61, grown from a melt with concentrations of cerium oxide ranging from 0. 1 to 1.6 wt%. A decrease of the Ce-crystal-melt distribution coefficie nt (C-Ce,C-crystal/C-Ce,C-melt), from 0.93 to 0.58, with increasing Ce concentrations in the melt was found. Furthermore, an increase of the Ba/Sr concentration-ratios (C-Ba/C-Sr) by (14 +/- 1%) from the crysta l with the lowest to the sample with the highest Ce content is observe d. With the assumption of a constant Nb concentration in all SBN-cryst als the experiments reveal an increase of the C-Ba/C-Nb ratio by (4 +/ - 2)% and a decrease of the C-Sr/C-Nb ratio by (7 +/- 2)% with increas ing Ce concentration in the melt. This produces a shift of the paramet er x in the SBN:Ce-formula from 0.61 to 0.57 +/- 0.02. The opposite tr end in the C-Ba/C-Nb and the C-Sr/C-Nb ratios with increasing Ce conte nts of the crystals indicates that Ce occupies Sr positions. The absor ption coefficient alpha(e) for extraordinarily polarized light increas es linearly with the increasing concentration C-Ce,C-crystal of Ce in the crystal. (C) 1997 Elsevier Science Ltd.