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

Abstract

In this work a radiospectroscopic investigation of the B-C, B-C-Ti and B-C-Cr systems was made in the range of 0 to 30 at % carbon at 4.2, 77 and 300 K. It is shown that in the B-C system, with a change of carbon 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 to 13% carbon and the second where the carbon content is 18 to 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 α-boron with one carbon atom. In the second range the experimental data indicate that probably the introduction of four carbon atoms occurs, so that the formation of B₁₂C₄ centres is in question. The change in intensity of the signal on introduction and increase of titanium and chromium 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.