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Structural changes of Bi 1.8 Sr 2 (<mml:math xmlns:mml="…

1991; American Physical Society; Volume: 43; Issue: 16 Linguagem: Inglês

10.1103/physrevb.43.13066

1095-3795

Takashi Onozuka, Yoshihiro Iwabuchi, Tetsuo Fukase, Hiroshi Sato, Terence E. Mitchell,

Iron-based superconductors research

The mode of the incommensurate modulation in the b direction of the ${\mathrm{Bi}}_{1.8}$${\mathrm{Sr}}_{2}$(${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Y}}_{\mathit{x}}$)${\mathrm{Cu}}_{2.2}$${\mathrm{O}}_{\mathit{z}}$ (0.05x0.75) system is investigated by means of electron diffraction and high-resolution lattice imaging. The change of period of the long-period structure with x is found to be basically due to the mixing ratio of domains of two modulation periods with b=4.5${\mathit{b}}_{0}$ and 5${\mathit{b}}_{0}$ or 4.5${\mathit{b}}_{0}$ and 4${\mathit{b}}_{0}$, thus creating periods of b=4.75${\mathit{b}}_{0--}$4.0${\mathit{b}}_{0}$. The fundamental orthorhombic lattice has dimensions of a\ensuremath{\simeq}b\ensuremath{\simeq}${\mathit{b}}_{0}$ (0.54 nm) and c\ensuremath{\simeq}${\mathit{c}}_{0}$ (3.1 nm). The change of the mixing mode from one to the other mentioned above occurs just in the yttrium concentration range, 0.45x0.65, which also corresponds to the superconductor (metallic)-to-semiconductor transition boundary. The mixing modes of the domains are directly recorded as a contrast modulation with half periods, 4.5${\mathit{b}}_{0}$/2 and 5${\mathit{b}}_{0}$/2 or 4.5${\mathit{b}}_{0}$/2 and 4${\mathit{b}}_{0}$/2 in high-resolution lattice images. These images are reproduced well by a multislice computer-simulation technique.