The NQR and NMR studies of icosahedral borides

Boron NMR and NQR studies have been performed on three icosahedral borides: alpha- and beta-rhombohedral boron and boron carbide(B12C3). Two B-11 NMR peaks, separated by significant chemical shifts in the range from 130 ppm t o 280 ppm, were clearly observed for all of the icosahedral borides that we re not enriched in the B-10 isotope. A single peak, however, was found for the B-10 enriched boron carbide powder (90.6 at.% enrichment.) Moreover, th e peak separation in the B-11 NMR spectrum for the unenriched beta-boron wa s reduced when the sample was crushed into a fine powder. In addition to NM R responses, four strong NQR responses were observed for boron carbides fro m different manufacturers. Two resonance signals, observed at 513 kHz and 2 769 kHz, correspond to one of the icosahedral boron sites and the boron in the CBC chain, respectively. The other two NQR responses, having frequencie s of 361 and 380 kHz, are either B-10 responses for the chain site or B-11 responses for the other boron sites in the icosahedra. The NQR responses ar e not only consistent with the previous NMR studies performed independently by Silver and Bray (1959 J. Chem. Phys. 31 247) and by Hynes and Alexander (1971 J. Chem. Phys. 54 5296, 1972 J. Chem. Phys. Erratum 56), but also pr ovide much higher accuracy for the values of the quadrupolar parameters.