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 ²⁷Al, ¹¹B 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 ¹¹B and ²⁷Al 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.