12046-91-2Relevant academic research and scientific papers
Radial X-Ray Diffraction Study of Superhard Early Transition Metal Dodecaborides under High Pressure
Lei, Jialin,Akopov, Georgiy,Yeung, Michael T.,Yan, Jinyuan,Kaner, Richard B.,Tolbert, Sarah H.
, (2019/04/08)
The deformation behavior of the three metal dodecaborides (YB12, ZrB12, and Zr0.5Y0.5B12) 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. Zr0.5Y0.5B12, which has the highest Vickers hardness (Hv = 45.8 ± 1.3 GPa at 0.49 N load), also shows the highest bulk modulus (K0 = 320 ± 5 GPa). The 0.49 N hardness for ZrB12 and YB12 are both lower and very similar, and both show lower bulk moduli (K0 = 276 ± 7 GPa, and K0 = 238 ± 6 GPa, respectively). Differential stress is then measured to study the strength and strength anisotropy. Zr0.5Y0.5B12 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} [(Formula presented.)]. Strain softening is also observed for ZrB12. Finally, the full elastic stiffness tensors for ZrB12 and YB12 are solved. ZrB12 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
Akopov, Georgiy,Mak, Wai H.,Koumoulis, Dimitrios,Yin, Hang,Owens-Baird, Bryan,Yeung, Michael T.,Muni, Mit H.,Lee, Shannon,Roh, Inwhan,Sobell, Zachary C.,Diaconescu, Paula L.,Mohammadi, Reza,Kovnir, Kirill,Kaner, Richard B.
, p. 9047 - 9062 (2019/06/13)
Single-phase metal dodecaboride solid solutions, Zr0.5Y0.5B12 and Zr0.5U0.5B12, were prepared by arc melting from pure elements. The phase purity and composition were established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and 10B and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to Zr1-xYxB12 were studied and it was found that carbon causes fast cooling and as a result rapid nucleation of grains, as well as "templating" and patterning effects of the surface morphology. The hardness of the Zr0.5Y0.5B12 phase is 47.6 ± 1.7 GPa at 0.49 N load, which is ～17% higher than that of its parent compounds, ZrB12 and YB12, with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr0.5U0.5B12 is ～54% higher than that of its UB12 parent. The dodecaborides were confirmed to be metallic by band structure calculations, diffuse reflectance UV-vis, and solid-state NMR spectroscopies. The nature of the dodecaboride colors - violet for ZrB12 and blue for YB12 - can be attributed to charge-transfer. XPS indicates that the metals are in the following oxidation states: Y3+, Zr4+, and U5+/6+. The superconducting transition temperatures (Tc) of the dodecaborides were determined to be 4.5 and 6.0 K for YB12 and ZrB12, respectively, as shown by resistivity and superconducting quantum interference device (SQUID) measurements. The Tc of the Zr0.5Y0.5B12 solid solution was suppressed to 2.5 K.
