Synthesis and Characterization of Single Phase Metal Dodecaboride Solid Solutions: Zr_1-xY_xB₁₂ and Zr_1-xU_xB₁₂

Journal Article · Tue May 07 00:00:00 EDT 2019 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.9b03482· OSTI ID:1514879

Akopov, Georgiy ^[1]; Mak, Wai H. ^[2]; Koumoulis, Dimitrios ^[2]; Yin, Hang ^[2]; Owens-Baird, Bryan ^[3]; Yeung, Michael T. ^[4]; Muni, Mit H. ^[2]; Lee, Shannon ^[3]; Roh, Inwhan ^[5]; Sobell, Zachary C. ^[6]; Diaconescu, Paula L. ^[2]; Mohammadi, Reza ^[7]; Kovnir, Kiril ^[3]; Kaner, Richard B. ^[2]

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1. Univ. of California, Los Angeles, CA (United States); Ames Lab. and Iowa State Univ., Ames, IA (United States)
2. Univ. of California, Los Angeles, CA (United States)
3. Ames Lab. and Iowa State Univ., Ames, IA (United States)
4. Northwestern Univ., Evanston, IL (United States)
5. Univ. of California, Los Angeles, CA (United States); Univ. of California, Berkeley, CA (United States)
6. Univ. of California, Los Angeles, CA (United States); Virginia Commonwealth Univ., Richmond, VA (United States)
7. Virginia Commonwealth Univ., Richmond, VA (United States)

Single-phase metal dodecaboride solid solutions, Zr_0.5Y_0.5B₁₂ and Zr_0.5U_0.5B₁₂, 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 Zr_1-xY_xB₁₂ 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_0.5Y_0.5B₁₂ 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 Zr_0.5U_0.5B₁₂ 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 (T_c) 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 T_c of the Zr_0.5Y_0.5B₁₂ solid solution was suppressed to 2.5 K.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1514879
• Report Number(s): IS-J-9937
• Journal Information: Journal of the American Chemical Society, Vol. 141, Issue 22; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY