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Li 2 B 12 Si 2 : The First Ternary Compound in the System Li/B/Si: Synthesis, Crystal Structure, Hardness, Spectroscopic Investigations, and Electronic Structure
Author(s) -
Vojteer Natascha,
Schroeder Melanie,
Röhr Caroline,
Hillebrecht Harald
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701949
Subject(s) - orthorhombic crystal system , raman spectroscopy , crystallography , crystal structure , materials science , band gap , ternary operation , tetragonal crystal system , electronic structure , electronic band structure , chemistry , condensed matter physics , computational chemistry , physics , programming language , optoelectronics , computer science , optics
We present the synthesis, crystal structure, hardness, IR/Raman and UV/Vis spectra, and FP‐LAPW calculations of the electronic structure of Li 2 B 12 Si 2 , 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 °C in h‐BN crucibles in arc‐welded Ta ampoules. Li 2 B 12 Si 2 crystallizes orthorhombic in the space group Cmce (no. 64) with a =6.1060(6), b =10.9794(14), c =8.4050(8) Å, and Z =4. The crystal structure is characterized by a covalent network of B 12 icosahedra connected by Si atoms and Li atoms located in interstitial spaces. The structure is closely related to that of MgB 12 Si 2 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 Li 2 B 12 Si 2 is a hard material. The band gap was determined experimentally and calculated by theoretical means. UV/Vis spectra 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.