OBSERVATION OF INTERGROWTH STRUCTURES OF HG-1212, HG-1223 AND HG-1234PHASES IN A NOMINAL HG-1223 CERAMIC SUPERCONDUCTOR

Intergrowth structures of the Hg-1223 superconductor containing other Hg superconducting phases such as Hg-1212 and Hg-1234 were observed un der a transmission electron microscope. The x-ray diffraction pattern, the resistance-temperature relationship and the a.c. magnetic suscept ibility-temperature relationships indicate that the sample contains ma inly Hg-1223 phase. However, scanning electron microscope and energy d ispersive x-ray analysis show that the sample contains intergrowth str uctures. In our previous joint work, two fundamental intergrowth struc tures were reported. Here we report two more intergrowth structures, n amely Hg-1223/(Hg-1212, Hg-1223, Hg-1234) and Hg-1223/(Hg-1223, Hg-123 4). Calculation of the ratio of strain energy density U-t and the Youn g modulus E(001) along the (001) direction of the unit cell of the Hg sample shows that the value of U-t/E(001) for the first region is 1.54 x 10(-4) and for the second is 1.56 x 10(-3). The reason for the form ation of the ill-defined mismatch region in the second intergrowth str ucture may be due to the relatively large strain field in the conjunct ion boundary of the structure.