Diffuse scattering in La-Sm-Sr-Cu-O

Diffuse scattering, reflecting structural disorder in La_1.8-xSm_xSr_0.2CuO_z, have been investigated by means of electron diffraction. In the T⋆-structure, in addition to the fundamental spots due to the T⋆-structure there exists cylindrical-shape diffuse scattering due to static displacements of the apical oxygen atoms in the CuO₅ pyramids. On the other hand, both thermal diffuse scattering and superlattice spots have been found in diffraction patterns obtained from the T-structure. The thermal diffuse scattering is distributed on the {100}⋆ planes of reciprocal space. In addition, the superlattice spots appear in a range of 0.3 < ϗ < 0.6 and are located at a zone boundary of the first Brillouin zone along the < 110 >⋆ directions. On the basis of the extinction rule for the superlattice spots, the crystal system of the T-structure for 0.3 < ϗ < 0.6 is concluded to be orthorhombic while the system for 0 < ϗ < 0.3 is tetragonal.