Determination of the crystal system and space group ofBaBiO3by convergent-beam electron diffraction and x-ray diffraction using synchrotron radiation

Abstract

The crystal system and space group of ${\mathrm{BaBiO}}_{3}$ with a distorted perovskite structure were investigated by convergent-beam electron diffraction (CBED), selected area electron diffraction, and x-ray diffraction using synchrotron radiation. Since all the observed CBED patterns showed a symmetry of 1, and the $\ifmmode\pm\else\textpm\fi{}G$ dark-field disk of CBED patterns indicated the absence of an inversion center in ${\mathrm{BaBiO}}_{3},$ the crystal symmetry of ${\mathrm{BaBiO}}_{3}$ was concluded to be triclinic with a space group of $P1$ (No. 1). The diffraction angles of the x-ray-diffraction peaks of ${\mathrm{BaBiO}}_{3},$ obtained using synchrotron radiation, could apparently be explained by assuming a monoclinic symmetry. However, a larger full width at half maximum (FWHM) of the 440 peak, indexed assuming a monoclinic symmetry other than that of each peak of 008, $404\ifmmode\bar\else\textasciimacron\fi{},$ 404, and 044 could not be explained. The large FWHM of the 440 peak could be attributed to an overlapping of the $4\ifmmode\bar\else\textasciimacron\fi{}40$ and 440 peaks of triclinic symmetry, showing agreement with the result of CBED.