Structural compression and vibrational properties ofBi12SiO20 sillenite from experiment and theory

Abstract

The crystal structure of the bismuth silicon oxideBi12SiO20 was determined by single-crystal x-ray diffraction at ambient conditions and at high pressure.Single-crystal intensity data between 0.0001 and 16.8(3) GPa were collected in house withMo Kα radiation and withsynchrotron radiation (λ = 0.45 Å) at HASYLAB (D3), while lattice parameters were measured up to 23.0(3) GPa. The largecavities which exist in the crystal structure and host the lone electron pairs of theBi3 + ions are considerably compressed at high pressure. The crystal structure,however, remains stable and the lone electron pair is stereochemically activeup to at least 16.8 GPa. A larger compression in the direction of the loneelectron pairs by shear deformation was not observed. Raman spectra ofBi12SiO20 were measured on powder samples during pressure decrease from 39.1(1) GPa down toambient pressure and on single crystals during pressure increase up to 12.50(3) GPa.Density functional perturbation theory was used to compute Raman frequencies andintensities at ambient pressure and to investigate pressure-induced changes up to 50 GPa.