Synthesis and characterization of aluminum diboride products using 27Al, 11B NMR and ab initio studies

Understanding different bonding environments in various metal borides provides insight into their structures and physical properties. Polycrystalline aluminum diboride (AlB2) samples have been synthesized and compared both with a commercial sample and with the literature. One issue that arose is the relative ease with which boron-rich and aluminum deficient phases of aluminum borides can be presented in AlB2. Here, we report Al-27, B-11 nuclear magnetic resonance (NMR) spectroscopy and first-principles calculations on AlB2 in order to shed light on these different bonding environments at the atomic level and compare the structural and electronic properties of the products of different preparations. Along with the aforementioned, the present study also takes an in-depth look at the nature of the B-11 and Al-27 nuclear spin-lattice relaxation recovery data for the AlB2 and other superhard materials. The nuclear spin-lattice relaxation has been measured for a static sample and with magic-angle spinning. The combination of NMR and band structure calculations highlights the synthetic challenges with superhard materials.