High pressure crystal structure and electronic properties of bismuth silicate Bi2SiO5 from synchrotron experiment and first principle calculations

The high pressure structural properties of bismuth oxide Bi2SiO5 have been investigated up to 28 GPa using in situ powder synchrotron X-ray diffraction and up to 50 GPa with DFT calculations. The monoclinic structure is found to persist up to about 20 GPa, where a notable change in the compressibility occurs. The DFT data imply that this is due to a second-order phase transition from the ambient condition monoclinic structure with space group Cc to an orthorhombic polymorph with space group Cmcm. This transition involves the straightening of the chains formed by corner-connected SiO4 tetrahedra, that suppresses the ferroelectricity in the high pressure, centrosymmetric phase of Bi2SiO5. The stereo-chemical activity of the Bi3+ lone electron pair is found to decrease with increasing pressure, but it can still be identifed in the calculated electron density difference maps at 50 GPa.