OXYGEN CENTERS IN STOICHIOMETRIC BAFBR AND INTRINSIC HOLE-CENTERS IN NONSTOICHIOMETRIC BAFBR

By means of electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements we found in stoichiometric BaFB r single crystals two additional oxygen centres. The first one is an O - ion on a bromide site, the second one consists of an oxygen molecula r ion O-2(-) with one oxygen atom on a bromide site and one on a neigh bouring fluoride site. In nonstoichiometric BaFBr powders we found a n ew room temperature stable hole centre. The powder EPR line can be sim ulated with the assumption that the it is an H-type F-2(-) centre on a fluoride site. This K-type centre is formed as a compensating hole ce ntre to the F(Br-) centre. (C) 1998 Elsevier Science Ltd. All rights r eserved.