Paramagnetic centers in boron and aluminum borides

The electron spin resonance spectra of crystalline and amorphous boron and aluminum dode-caboride samples have been recorded on a Q-band spectrometer. The parameters of the spectra have been determined, and the concentration of paramagnetic centers has been estimated. It has been found that the concentration of the paramagnetic centers in amorphous boron is high and exceeds the corresponding value in crystals by two orders of magnitude. The spectra of boron powders enriched in 11B and 10B isotopes have been measured. It has been established that the difference between the hyperfine interactions of the unpaired electron with the 11B and 10B nuclei manifests itself as a change in the width of the structureless electron spin resonance spectra.