Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr 1- x Y x B 12 and Zr 1- x U x B 12

• Published in: Journal of the American Chemical Society 2019-06, Vol.141 (22), p.9047-9062
• 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, Kirill, Kaner, Richard B
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b03482

Single-phase metal dodecaboride solid solutions, Zr Y B and Zr U B , 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 B and B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to Zr Y B 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 Zr Y B phase is 47.6 ± 1.7 GPa at 0.49 N load, which is ∼17% higher than that of its parent compounds, ZrB and YB , with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr U B is ∼54% higher than that of its UB 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 ZrB and blue for YB -can be attributed to charge-transfer. XPS indicates that the metals are in the following oxidation states: Y , Zr , and U . The superconducting transition temperatures ( T ) of the dodecaborides were determined to be 4.5 and 6.0 K for YB and ZrB , respectively, as shown by resistivity and superconducting quantum interference device (SQUID) measurements. The T of the Zr Y B solid solution was suppressed to 2.5 K.