화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.141, No.22, 9047-9062, 2019
Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1-xYxB12 and Zr1-xUxB12
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 B-10 and B-11 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 similar to 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 similar to 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 (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 Zr0.5Y0.5B12 solid solution was suppressed to 2.5 K.