title: Experimental determinations and quantum-chemical calculations of the vibrational spectra of β-ZnB4O7 and β-CaB4O7.
abstract: The two oxoborates β-ZnB4O7 and β-CaB4O7 were synthesized and investigated by FTIR- and Raman spectroscopy and ab initio quantum chemical calculations. Maximum and mean deviations between experimentally determined bands and calculated modes ranged between 15-36 cm(-1) and 5-7 cm(-1), respectively, allowing band assignments to vibrational modes in most cases. The complex network structures with tetrahedral BO4 and planar OB3 groups are mirrored by the spectra and numerous vibrational modes, not assignable by standard borates classification schemes. It was confirmed that OB3 units, despite similar force constants and geometry, do not absorb in the same range as BO3 units. Bands in the high wavenumber range are rather caused by B-O-(Zn/Ca), O-B-O, B-O-B, and B-O stretching and bending vibrations. The experimental observation of inactive or Raman-active modes in the absorption spectra indicates defects or structural distortions in both compounds.
authors: MATERIALS- Institute for Surface Technologies and Photonics, JOANNEUM RESEARCH, Leobner Strasse 94, A-8717 Niklasdorf, Austria. Electronic address: reinhard.kaindl@joanneum.at.
authors: Reinhard
authors: R
authors: Kaindl
authors: Gerhard
authors: G
authors: Sohr
authors: Hubert
authors: H
authors: Huppertz
mesh_terms: D001881:Borates / Q000737:chemistry*; D008958:Models, Molecular; D017601:Oxygen Compounds / Q000737:chemistry*; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman
chemical_list: D001881:Borates; D017601:Oxygen Compounds
keywords: Ab initio; FTIR; High-pressure oxoborate; Quantum chemical calculation; Raman spectroscopy