10B and 11B high-resolution NMR studies on boron-doped diamond

11 B magic-angle spinning (MAS) NMR experiments are applied to B-doped diamond samples prepared by high-pressure and high-temperature methods. From the spectrum, we show that there are at least four boron signal components and the one at 28.5 ppm is ascribed to the substitutional boron in the diamond structure providing the carriers responsible for conductivity. We further apply two-dimensional (2D) NMR to examine 1 H dipolar broadening and 11 B– 11 B boron spin diffusion, and candidates purported so far for the excess boron, that is, a boron + hydrogen complex and –B–B– and/or –B–C–B– clusters are negated. Furthermore, we show that 10 B MAS NMR is useful to selectively observe the substitutional boron in the diamond structure appearing at 28.5 ppm, whose quadrupolar coupling is much smaller than that of the excess boron at 65.5 ppm.