Synthesis and characterization of single-crystal strontium hexaboride nanowires

Growth Mechanism of SmB6 Nanowires Synthesized by Chemical Vapor Deposition: Catalyst-Assisted and Catalyst-Free

SmB₆ nanowires, as a prototype of nanostructured topological Kondo insulator, have shown rich novel physical phenomena relating to their surface. Catalyst-assisted chemical vapor deposition (CVD) is a common approach to prepare SmB₆ nanowires and Ni is the most popular catalyst used to initiate the growth of SmB₆ nanowires. Here, we study the effect of growth mechanism on the surface of SmB₆ nanowires synthesized by CVD. Two types of SmB₆ nanowires are obtained when using Ni as the catalyst. In addition to pure SmB₆ nanowires without Ni impurity, a small amount of Ni is detected on the surface of some SmB₆ nanowires by element analysis with transmission electron microscopy. In order to eliminate the possible distribution of Ni on nanowire surface, we synthesize single crystalline SmB₆ nanowires by CVD without using catalyst. The difference between catalyst-assisted and catalyst-free growth mechanism is discussed.

Nanostructuring of Strontium Hexaboride via Lithiation

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, Li_xSr_1-2xB₆, 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 <100 nm SrB₆ 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.

Synthesis, and magnetic and optical properties of nanocrystalline alkaline-earth hexaborides

Cubic-shaped ultrafine alkaline-earth hexaborides (MB₆, M = Ca, Ba, Sr) have been synthesized via a solid-state reaction of MO with NaBH₄ at 1150 °C.

Nano-ceramic support materials for low temperature fuel cell catalysts

Low temperature fuel cells (LTFCs) have received broad attention due to their low operating temperature, virtually zero emissions, high power density and efficiency. However, the limited stability of the catalysts is a critical limitation to the large scale commercialization of LTFCs. State of the art carbon supports undergo corrosion under harsh chemical and electrochemical oxidation conditions, which results in performance degradation of catalysts. Therefore, non-carbon materials which are highly oxidation resistant under strongly oxidizing conditions of LTFCs are ideal alternative supports. This minireview highlights the advances and scenarios in using nano-ceramics as supports to enhance the stability of catalysts, the solutions to improve electrical conductivity of nano-ceramic materials, and the synergistic effects between metal catalyst and support to help improve the catalytic activity and CO/SO2 tolerance of catalysts.