Superstructure determination of the perovskite βLa0.33NbO3

Abstract

New interesting results in the crystal structure of the perovskite βLa_0.33NbO₃ were revealed using selected area electron diffraction, powder X-ray diffraction techniques and Rietveld refinement method. Although the superstructure of βLa_0.33NbO₃ could not be seen by conventional X-ray powder diffraction technique, the electron diffraction patterns revealed weak spots resulting in a superstructure array for the atoms of βLa_0.33NbO₃. The crystal symmetry is compatible with an orthorhombic cell, space group Cmmm. From Rietveld refinement, the resulting lattice parameters are: a = 7.82(1) Å, b = 7.83(9) Å, c = 7.90(9) Å and goodness of fit R = 0.1107, Rwp = 0.15. The superstructure is built from distorted octahedra NbO₆ along the [001] axis. Results suggest that this distortion may be produced by occupation of La atoms in (2a) and (4l) sites.