Probing for Structural Features of Boron‐rich Solids with EELS

Crystal structures of boron‐rich solids are characterized by boron atom arrangements that are quite diverse: chains, sheets, and a variety of polyhedra like octahedra, pentagonal bipyramids, cuboctahedra, and icosahedra are observed. Probing by electron energy‐loss spectroscopy (EELS), these different structural features are mirrored by a pronounced variation of the energy loss near‐edge fine structure (ELNES) of the B_K ionization edges. For identification, characteristics of these fine structures can be used as so‐called “coordination fingerprints”, which is shown for solids like MgB₂, TaB₂, ZrB₂, CaB₆, SrB₆, BaB₆, NaB₅C, KB₅C, Na₃B₂₀, Na₂B₂₉, UB₁₂, ZrB₁₂, LaB₂C₂, CeB₂C₂, and CaB₂C₂. In addition, theoretical calculations of ELNES based on the density functional theory (FLAPW method) are presented for an example of boron‐rich solids.