EPR observation of anomalous triplet states in Ba1-xKxBiO3 and BaPbyBi1-yO3 systems

The experimental data on electronic paramagnetic resonance (EPR) signals in Ba1-xKxBiO3 (BKBO) and BaPbyBi1-yO3 (BPBO) systems are represented. The sy stematic EPR study has been performed for samples in the wide ranges of dop ing levels (0 < x < 0.5, 0 < y < 1) and temperature intervals. All the samp les were diamagnetic. Beside the EPR resonances with g approximate to 2.1, the additional 'half-field' signals with g approximate to 4.2 was detected. These signals indicate the existence of tripler states of localized charge pairs. The signals with g approximate to 4.2 were observed only for high q uality samples with special attention preventing the oxygen escape from the samples during experiment. The results are explained by partial disorder o f ordered Bi-O covalent bonds. Such disordered state form the singlet and e xcited triplet states in forbidden energy band of studied oxide systems. (C ) 1999 Elsevier Science B.V. All rights reserved.