High-pressure compressibility and electronic properties of bismuth silicate Bi2SiO5 from synchrotron experiments and first-principles calculations

The high-pressure structural properties of bismuth oxide Bi2SiO5 have been investigated up to 29 GPa using in situ powder synchrotron x-ray diffraction (XRD) and up to 50 GPa with density functional theory (DFT) calculations. We found a compressibility anomaly at about 20 GPa that is observed both in our XRD and DFT results. The rotation of the corner-connected SiO4 tetrahedra produces a straightening of the silicate chains, yielding a lower compressibility above 20 GPa for the structure with straight chains. We analyzed the stereochemical activity of the Bi3+ lone electron pair, which is found to decrease with increasing pressure, but it can still be identified in the calculated electron density difference maps at 50 GPa.