¹¹B NMR Spectral and Nuclear Spin–Lattice Relaxation Analyses of ReB₂

Abstract

Analyses of the one-dimensional 11B NMR spectra from static and MAS experiments of a polycrystalline ReB2 sample have extracted parameters characterizing both the electric field gradient and the shielding at the boron site. In contrast to that previously assumed for AlB2, the principal axis systems for these two interactions are not coincident in ReB2. A brief discussion of the literature regarding spin–lattice relaxation for half-integer quadrupolar nuclei and the mathematical functions used for the extraction of relaxation time constants is presented. With radiofrequency conditions chosen to excite the central and satellite transitions, the saturation recovery spin–lattice relaxation rate of ReB2 is better described by a single exponential rather than the Andrew–Tunstall multiexponential model for I = 3/2. In addition, relaxation measurements for 11B in ReB2 have been extended to temperatures above ambient and show a deviation from the Korringa relationship.

11B NMR Study of WB2

“…Figure shows the 11 B NMR spectrum of a static polycrystalline sample of WB 2 at 296 K. The full width at half-height of this resonance at 19.7 kHz is quite similar to that observed for the central transition in ReB 2 of 20.2 kHz and in AlB 2 of 21.8 kHz. However, the difference in spectra for these compounds is more readily apparent in the MAS experiments.…”

“…Transition metal borides can display many different bonding environments as the interactions between boron and metal atoms vary within the different structures. Numerous 11 B NMR studies of various metal diborides with both the AlB 2 -type − and ReB 2 -type − structures have been reported in the literature. However, the present 11 B NMR study is the first to investigate boron sites arising from the differing structural motif of WB 2 .…”

DFT prediction of a novel molybdenum tetraboride superhard material

“… 1–9 Over the last few years, a large number of TMBs have been widely investigated. 10–15 Despite some TMBs being potential superhard materials, 16,17 controversy remains about the intrinsic hardness of TMBs. One is that the measured Vickers hardness of TMBs fails to agree with the theoretical results.…”

The influence of high pressure on the structural stability, Vickers hardness and mechanical properties of Re and Ru dodecaborides

“…[1][2][3][4][5][6][7][8] In comparison to the conventional superhard materials (diamond and boron nitride), transition metal borides (TMBs) are promising superhard materials. [15][16][17] For example, the calculated bulk modulus and shear modulus of ReB 2 are 369.2 and 294.9 GPa, respectively. [15][16][17] For example, the calculated bulk modulus and shear modulus of ReB 2 are 369.2 and 294.9 GPa, respectively.…”

“…[9][10][11][12][13][14] Those TMBs not only show the high hardness and elastic modulus but also exhibit better electronic properties. [15][16][17] For example, the calculated bulk modulus and shear modulus of ReB 2 are 369.2 and 294.9 GPa, respectively. [18] The calculated bulk modulus and shear modulus of WB 2 are 338 and 275 GPa, respectively.…”