Phase transitions and twin lamellae in the (Bi,Pb)2223 phase: in situ high temperature electron diffraction studies

✍ Scribed by N.D. Zhigadlo; M. Czank; W. Depmeier

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 360 KB
• Volume: 400
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2003.06.001

✦ Synopsis

Phase transitions and twin lamellae of the (Bi,Pb)2223 phase have been studied by in situ heating experiments in a transmission electron microscope over a range of temperatures 293-800 K. In some crystal grains of the (Bi,Pb)2223 phase a modulation with the modulation wave vector q ffi 0:137b à (Pb-type) was observed with 1st order satellites associated with the [0 0 1] zone. Furthermore, a monoclinic distortion was observed, as indicated by splitting of the reflections in the b à direction. The monoclinicity was confirmed by dark-field images, which showed (1 0 0) twin lamellae. Diffuse streaks along hh h 0i are present in some crystals already at room temperature, but appear in others at temperatures below 365 K. Their intensities sharpen with increasing temperature, and at 630 K a 2a  2b superstructure appears. At the same temperature the monoclinic distortion and the twin lamellae disappear gradually. The new 2a  2b superstructure and Pb-type modulations coexist until the phase starts to decompose. The change of these structural modulations and twin transformations are discussed in connection with oxygen ordering within the different structural layers.