Li2B12Si2: The first ternary compound in the system Li/B/Si: Synthesis, crystal structure, hardness, spectroscopic investigations, and electronic structure

摘要

We present the synthesis, crystal structure, hardness, IR/Raman and UV/Vis spectra, and FP-LAPW calculations of the electronic structure of Li2B12Si2, the first ternary compound in the system Li/B/Si. Yellow, transparent single crystals were synthesized from the elements in tin as solvent at 1500 degrees C in h-BN crucibles in arc-welded Ta ampoules, Li2B12Si2 crystallizes orthorhombic in the space group Cmce (no.64) with a = 6.1060(6), b = 10.9794(14), c = 8.4050(8) angstrom, and Z = 4. The crystal structure is characterized by a covalent network of B-12 icosahedra connected by Si atoms and Liatoms located in interstitial spaces. The structure is closely related to that of MgB12Si2 and fulfils the electron-counting rules of Wade and Longuet-Higgins. Measurements of Vickers (H-v = 20.3 Gpa) and Knoop microhardness (H-k = 20.4 GPa) revealed that Li2B12Si2 is a hard material. The band gap was determined experimentally and calculated by theoretical means. UV/Visspectra revealed a band gap of 2.27 eV. with which the calculated value of 2.1 eV agrees well. the IR and Raman spectra show the expected oscillations of icosahedral networks. Theoretical investigations of bonding in this structure were carried out with the FP-LAPW method. The results confirm the applicability of simple electron-counting rules and enable some structural specialties to be explained in more detail.