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.