Analysis of large-area twins in ${\mathrm{Bi}}_2$${\mathrm{CaSr}}_2$${\mathrm{Cu}}_2$${\mathrm{O}}_8$ superconductors

We report on large-area twin structures in ${\mathrm{Bi}}_2$ ${\mathrm{CaSr}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$. Crystal growth was by a self-fluxed method. Twins were extracted from the free surfaces of the resolidified flux. Twinning was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy and the twins were determined to be growth twins with {110} twin boundaries. Details of twin morphology and structure are presented in the context of twin formation and growth. Superconducting properties of the twinned specimens were determined by electrical and magnetic measurements. Preliminary results indicate that a single twin boundary did not significantly affect the resistance-temperature characteristics. Growth steps on the (001) face (which necessitated current transport in the c direction) were more important in determining the sharpness and form of the resistive transition.