文摘
Elemental boron typically exists in either of two states: crystalline or amorphous. In the synthesis of boron-based superhard materials, such as WB<sub>4sub>, elemental boron is in some instances a side product that is difficult to separate from the desired superhard material. In the present study, both crystalline and amorphous boron are characterized by <sup>10sup>B and <sup>11sup>B nuclear magnetic resonance spectroscopy as a prelude for the study of boron-based superhard materials. The <sup>11sup>B spectrum of a static sample reflects both bulk magnetic susceptibility and second-order quadrupolar line shapes of quadrupolar frequencies ranging from 0 to 680 kHz. The <sup>10sup>B spectrum of a static sample shows quadrupolar frequencies ranging from 0 to 142 kHz. In contrast to the previous literature indicating relaxation of quadrupolar origin, the variable temperature spin鈥搇attice relaxation data indicate that the <sup>11sup>B relaxation at 248 K and below is dominated by spin diffusion from paramagnetic centers. Above 248 K, relaxation is dominated by a thermally activated interaction with the conduction charge carriers originating from the boron vacancies. Relaxation in amorphous elemental boron shows an additional insulating component with a comparatively long time constant of 44 s.