EPR OBSERVATION OF LOCALIZED HOLE PAIRS IN BKBO AND BPBO SYSTEMS

The systematic EPR study of BKBO and BPBO samples with a wide range of doping has been performed. For all the samples (with the exception of overdoped metallic BPBO) two resonances with g approximate to 2.1 and g approximate to 4.2 were detected which is a signature of triplet st ates in the system. We attribute these resonances to triplet hole pair s localized on the apical oxygens in accordance with the model of ''or dered hole bonds''. A least-squares fitting of the temperature depende nce for the line intensity yields the value of the exchange constant J (p) for the hole pair as well as paramagnetic Curie temperature theta which is characteristic of the interaction between those tripler pairs .