Features of structural fluctuations in superconducting oxides Ln{single bond}Ce{single bond}Cu{single bond}O (Ln {double bond, long} Pr, Nd)

Features of both crystal structures and structural fluctuations in superconducting oxides, Ln_2-xCe_xCuO_4-y (Ln {double bond, long} Pr, Nd) with 0 ≤ x ≤ 0.20, have been examined in detail by means of electron diffraction. In electron diffraction patterns of Ln_2-xCe_xCuO_4-y (Ln = Pr, Nd), there commonly exists characteristic diffuse scattering in addition to fundamental spots due to the T′-structure. The diffuse scattering is observed as a spike shape along the <110> directions around the fundamental spot. Because of no temperature dependence of the intensity of the scattering, the scattering is understood to be mainly due to static displacements of atoms. In addition, the electron-beam irradiation results in two effects in diffraction patterns. One is characterized by the appearance of superlattice spots in both Nd_2-xCe_xCuO_4-y and Pr_2-xCe_xCuO_4-y. That is, the irradiation produces the modulated structure due to the ordering of oxygen vacancies. The other is the splitting of the fundamental spot in Pr_2-xCe_xCuO_4-y, which is due to a twinning resulting from a structural transition.