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

• Published in: Journal of the American Chemical Society 2019-06, Vol.141 (22)
• Main Authors: 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, Kiril, Kaner, Richard B.
• Format: Article
• Language: English
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b03482

Single-phase metal dodecaboride solid solutions, Zr0.5Y0.5B12 and Zr0.5U0.5B12, were arranged 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 applied to charge-transfer. XPS indicates that the metals are in the following oxidation states: Y3+, Zr4+, and U$^{{5+}/^{6+}}$. 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.