Possible structural phase transition near 210 K of single-phase Bi(Pb)-Sr-Ca-Cu-O superconducting ceramics

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Abstract
Ultrasonic measurements on 2:2:1:2 and 2:2:2:3 single-phase samples of Bi-Sr-Ca-Cu-O and BiPb-Sr-Ca-Cu-O have been carried out. It was found for the first time that there is an anomalous structure change near 210 K in these Bi-based superconducting ceramics. Detailed studies revealed that the sudden change in sound attenuation and velocity is an isothermal-like process. Thermal analysis and specific-heat measurements proved that this anomalous change has characteristics of a phase transition. X-ray diffraction experiments showed sudden increases in lattice constants a and c indicating some fine-structure changes during this transition.