Infrared spectrum of synthetic isotopic species of sinhalite MgAlBO4

The i.r. spectra of isotopic species of synthetic sinhalite, MgAlBO4, are reported and discussed in relation with a group theoretical analysis. The stretching vibrations of the BO4 group are observed in the 1150-800 cm-1 region, but no significant 10B-11B isotopic shift is observed in the lower wavenumber region: the identification of the BO4 bending vibrations is thus impossible; these vibrations are very probably mixed up with lattice vibrations. Several translational modes of the Mg cations have been identified in the 500-300 cm-1 region with the help of 24Mg-26Mg isotopic shifts. The possible assignments for Al translations are also discussed. The large splitting of the ν3 components of the BO4 tetrahedron is discussed in connection with the vibrational behavior and the structure of other olivine-type compounds. © 1985.