Radial X‐Ray Diffraction Study of Superhard Early Transition Metal Dodecaborides under High Pressure

Abstract

The deformation behavior of the three metal dodecaborides (YB 12 , ZrB 12 , and Zr 0.5 Y 0.5 B 12 ) is investigated using radial X-ray diffraction under nonhydrostatic compression up to ≈60 GPa with a goal of understanding how bonding and metal composition control hardness. Zr 0.5 Y 0.5 B 12 , which has the highest Vickers hardness (Hv = 45.8 ± 1.3 GPa at 0.49 N load), also shows the highest bulk modulus (K 0 = 320 ± 5 GPa). The 0.49 N hardness for ZrB 12 and YB 12 are both lower and very similar, and both show lower bulk moduli (K 0 = 276 ± 7 GPa, and K 0 = 238 ± 6 GPa, respectively). Differential stress is then measured to study the strength and strength anisotropy. Zr 0.5 Y 0.5 B 12 supports the highest differential stress, in agreement with its high hardness, a fact that likely arises from atomic size mismatch between Zr and Y combined with the rigid network of boron cages. The (200) plane for all samples supports the largest differential strain, while the (111) plane supports the smallest, consistent with the theoretically predicted slip system of {111} [ 1 11 12 2 ]. Strain softening is also observed for ZrB 12 . Finally, the full elastic stiffness tensors for ZrB 12 and YB 12 are solved. ZrB 12 is the most isotropic, but the extent of elastic anisotropy for all dodecaborides studied is relatively low due to the highly symmetric boron cage network.

Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1–xYxB12 and Zr1–xUxB12

“…Zr:13B and Y:13B, respectively, at K0 = 276 ± 7 GPa (k'0 = 2.0 + 0.4) and K0 = 238 ± 6 GPa (k'0 = 3.0 + 0.1). 67 The solid solution supports the highest differential stress, due to the differences in the radii of Zr and Y and the boron cages. 67 Upon Figure S14), it is offset by the formation of superhard B4C (Figure S14), resulting in larger error bars (Figure 7).…”

“…67 The solid solution supports the highest differential stress, due to the differences in the radii of Zr and Y and the boron cages. 67 Upon Figure S14), it is offset by the formation of superhard B4C (Figure S14), resulting in larger error bars (Figure 7). A more complete picture of the Vickers hardness change for the (Zr1-xYx):Cz:13B system, with the simultaneous variation of both metal and carbon concentrations, can be seen in the 2D contour plots in Figure 13 (complete list of hardness and error values can be seen in Table S1).…”

Fabrication of Alkali Metal Boride: Honeycomb‐Like Structured NaB4 with High Hardness and Excellent Electrical Conductivity

“…Therefore, novel hard and superhard materials with high electrical transport properties are continuously attracting interest in searching next‐generation electronics for potential applications under extreme conditions. [ 7–11 ] Boron is a unique element that can establish strong covalent BB bonds [ 12 ] and also be readily bonded with both heavy transition metals (TM) [ 2,13–16 ] and light alkali metals (AM) like sodium (Na) and kalium (K) [ 17–19 ] to form unusual borides. For the past decades, TM borides (TMB) have attracted great attention to fabricating novel hard materials by introducing TM atoms into the short and highly covalent bonds of boron.…”

Design and Synthesis of Clathrate LaB8 with Superconductivity

“…With different guest atoms, MB 12 exhibits properties such as super-hardness (above 40 GPa for ZrB 12 [5] and Zr 0.5 Y 0.5 B 12 [6]), superconductivity (at 4.7 K for YB 12 and 5.8 K for ZrB 12 [7]), and oxidation resistance (at ∼695 • C for Y 0.5 Sc 0.5 B 12 [8]), making them of broad interest for industrial application. Studies of B-based clathrate materials seem to have focused mainly on guest-atom substitution [6,9]. However, the host cage may also play a vital role in determining material properties with, for example, YH 6 with H 24 cages and YH 9 with H 28 cages (the recently high-pressure synthesized clathrate superhydrides) having superconductivity at 227 K [10,11] and 243 K [11,12], respectively, which are closely related to the high H-derived electron density of states at the Fermi level.…”