- Nanostructuring of Strontium Hexaboride via Lithiation
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We describe the top-down nanostructuring of a metal boride using SrB6 as an example. To accomplish this transformation, we demonstrate (1) the direct lithiation of a metal boride using n-butyllithium and then (2) the reactive disassembly of Li-SrB6 into nanoparticles using water. The identity of the Li-SrB6 intermediate, a mixture of Li2B6, LixSr1-2xB6, and SrB6 phases, was established by powder X-ray diffraction (PXRD), solid-state 11B and 7Li NMR, transmission electron microscopy, selected-area electron diffraction, and scanning electron microscopy. The necessary 2Li+/Sr2+ substitution is enabled by cation mobility within the hexaboride lattice. The subsequent reaction with water results in Li2B6 decomposition and the release of 6 nanoparticles, which were characterized by PXRD, solid-state 11B and 7Li NMR, and high-resolution TEM. This chemistry opens new solution-based modification and processing options for metal borides.
- Ramachandran, Roshini,Salguero, Tina T.
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- Formation and properties of SrB6 single crystals synthesized under high pressure and temperature
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Pure SrB6 single crystals are synthesized under high pressure (5 GPa) and temperature (1300 °C). The structure and morphology of the SrB6 single crystals are characterized by X-ray diffraction and field emission scanning electron microscope. The lattice constant of the SrB 6 crystals with a space group of Pm-3m is a = 4.1975. The dependence of electric resistivity and Hall coefficient on temperatures from 2 to 300 K show that the SrB6 single crystals are conductive materials with semi-metallic behavior and can be considered as electronic current carriers. The results of the band structure calculation show that the conduction and valence bands meet at the X point at the Fermi Level, which is consistent with the experimentally measured conducting behavior of SrB6 single crystals. The total and partial density of states show that the states at the Fermi level come from the 2p orbitals of the B atoms and the 4d orbital of the Sr atom. The magnetization measurement shows the diamagnetic nature of the SrB6. The nanoindentation measurement indicates that the hardness of SrB6 reached 33 GPa.
- Xin, Shengwei,Liu, Shaocun,Wang, Nan,Han, Xianyue,Wang, Limin,Xu, Bo,Tian, Yongjun,Liu, Zhongyuan,He, Julong,Yu, Dongli
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- Hydrogen storage properties of LiBH4 destabilized by SrH 2
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In this work, we have succeeded in destabilizing LiBH4 by the addition of SrH2, via the reaction 6LiBH4 + SrH 2 → SrB6 + 6LiH + 10H2 with a theoretical hydrogen capacity of 9.1 wt.%. According to the van't Hoff and Arrhenius equations, the dehydrogenation enthalpy change and activation energy for the LiBH4/SrH2 system were experimentally determined to be 48 kJ/mol H2 and 64 kJ/mol, respectively. Both are remarkably reduced in comparison with the pristine LiBH4, which is responsible for the improved dehydrogenation property of the LiBH4/SrH2 system. The dehydrogenated products SrB6 + 6LiH can be rehydrogenated to form LiBH4 and LiSrH3 at 723 K under an initial hydrogen pressure of 8.0 MPa.
- Liu,Huang,Si,Zhang
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- Novel alkali earth borohydride Sr(BH4)2 and borohydride-chloride Sr(BH4)Cl
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Two novel alkali earth borohydrides, Sr(BH4)2 and Sr(BH4)Cl, have been synthesized and investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and Raman spectroscopy. Strontium borohydride, Sr(BH4)2, was synthesized via a metathesis reaction between LiBH4 and SrCl2 by two complementary methods, i.e., solvent-mediated and mechanochemical synthesis, while Sr(BH4)Cl was obtained from mechanochemical synthesis, i.e., ball milling. Sr(BH4)2 crystallizes in the orthorhombic crystal system, a = 6.97833(9) A, b = 8.39651(11) A, and c = 7.55931(10) A (V = 442.927(10) A3) at RT with space group symmetry Pbcn. The compound crystallizes in α-PbO2 structure type and is built from half-occupied brucite-like layers of slightly distorted [Sr(BH4)6] octahedra stacked in the a-axis direction. Strontium borohydride chloride, Sr(BH4)Cl, is a stoichiometric, ordered compound, which also crystallizes in the orthorhombic crystal system, a = 10.8873(8) A, b = 4.6035(3) A, and c = 7.4398(6) A (V = 372.91(3) A3) at RT, with space group symmetry Pnma and structure type Sr(OH)2. Sr(BH4)Cl dissociates into Sr(BH4)2 and SrCl2 at ～170 C, while Sr(BH4)2 is found to decompose in multiple steps between 270 and 465 C with formation of several decomposition products, e.g., SrB 6. Furthermore, partly characterized new compounds are also reported here, e.g., a solvate of Sr(BH4)2 and two Li-Sr-BH 4 compounds.
- Ravnsbaek,Nickels,Cerny,Olesen,David,Edwards,Filinchuk,Jensen
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p. 10877 - 10885
(2013/10/22)
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- Improvement of thermoelectric properties of alkaline-earth hexaborides
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Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of
- Takeda, Masatoshi,Terui, Manabu,Takahashi, Norihito,Ueda, Noriyoshi
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p. 2823 - 2826
(2008/10/09)
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- Thermoelectric properties of some metal borides
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Polycrystalline AlMgB14 and some hexaborides (CaB6, SrB6, YbB6, SmB6, and CeB6) were synthesized to examine their thermoelectric properties. Single phase of orthorhombic AlMgB14, which contains B12 icosahedral clusters as building blocks, was obtained at sintering temperatures between 1573 and 1823K. Seebeck coefficient (α) and electrical conductivity (σ) of the phase were about 500μV/K and 10-11/Ωm at room temperature, respectively. These values are comparable to those of metal-doped β-rhombohedral boron. On the other hand, metal hexaborides with divalent cation possessed large negative α ranging from -100 to -270μV/K at 1073K. Calculated power factors of CaB6 and SrB 6 exceeded 10-3W/K2m within the entire range of temperature measured. As a result, they can be thought as promising candidates for n-type thermoelectric material.
- Takeda, Masatoshi,Fukuda, Tadahiro,Domingo, Ferrer,Miura, Takahiro
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p. 471 - 475
(2008/10/09)
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- On the existence of solid solutions based on magnesium diboride
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Dense samples of pure magnesium boride and of the compositions Mg (1-x) AxB2 (A = Na, K, Ca, Sr, Ba, Sn, Ti; 0. 05 2 samples vary only slightly as compared to those of the pure MgB2 irrespective of the sample preparation procedure, high temperature-high pressure treatment conditions, and the amount of dopant, thus indicating the absence of extended solid solution regions. The superconducting transition temperatures of all the samples did not exceed the value characteristic of MgB2 (39±1 K). The results obtained for the dense MgB2 samples using the Andreev reflection and tunneling spectroscopies confirm the two-gap nature of superconductivity in magnesium diboride and point to analogy between the superconductivity mechanisms in this compound and in cuprates.
- Sevast'yanova,Kazin,Kravchenko,Kuz'michev,Ponomarev,Burdina,Bulychev
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p. 1674 - 1680
(2007/10/03)
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- Reactivity of MgB2 with common substrate and electronic materials
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The reactivity of MgB2 with powdered forms of common substrate and electronic materials is reported. Reaction temperatures between 600 and 800°C, encompassing the range commonly employed in thin-film fabrication, were studied. The materials tes
- He,Cava,Rowell, John M.
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p. 291 - 293
(2008/10/08)
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