The structure of paramagnetic centres and the formation of defects in the B-C, B-C-Ti and B-C-Cr systems

A radiospectroscopic investigation of the B--C, B--C--Ti and B--C--Cr systems was made in the range of 0-30 at.-% carbon at 4.2, 77 and 300 deg K. It is shown that in the B--C system, with a change of C content from 0 to 30%, there are two concentration ranges in which a change occurs in the character of EPR signal: the first from 0-13% C and the second where the C content is 18-30%. The g factor, the width, the form and the intensity of EPR lines indicate that in the first range the EPR signal is due to the B12C complexes, which represent the lattice of alpha -B with one C atom. In the second range the experimental data indicate that probably the introduction of four C atoms occurs, so that the formation of B12C4 centers is in question. The change in intensity of the signal on introduction and increase of Ti and Cr contents indicates different mechanisms of interaction of the basic components in this system. Keeping in mind that with increasing content of addition the microhardness of samples increases, while the intensity of the EPR signal decreases, it is probable that larger amounts of the B13C2-phase, which is characterized by a higher microhardness, are then formed.9 refs.--AA