10B and 11B NMR Study of Elemental Boron

详细信息    查看全文

• 作者：Christopher L. Turner ; R. E. Taylor ; Richard B. Kaner
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：June 18, 2015
• 年：2015
• 卷：119
• 期：24
• 页码：13807-13813
• 全文大小：348K
• ISSN：1932-7455

文摘

Elemental boron typically exists in either of two states: crystalline or amorphous. In the synthesis of boron-based superhard materials, such as WB₄, 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 ¹⁰B and ¹¹B nuclear magnetic resonance spectroscopy as a prelude for the study of boron-based superhard materials. The ¹¹B 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 ¹⁰B 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 ¹¹B 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.