Highly textured and single crystal Bi2CaSr2Cu2Ox prepared by laser heated float zone crystallization

Abstract A CO 2 laser heat source was used to float zone 0.36 cm diameter ceramic rods of Bi 2 CaSr 2 Cu 2 O x . Well behaved, stable molten zones were obtained in air and in O 2 pressures up to 2.6 atm. Highly textured elongated grains ∼ 1 cm long with the c -axis normal to the rod axis were obtained at slow (0.19 cm/h) growth rates. Crystals 3×1.2×0.3 mm were easily cleaved from such specimens. In the best cases (slow growth rates), X-ray powder diffraction indicated ∼ 100% Bi 2 CaSr 2 Cu 2 O x , the superconducting transition temperature was as high as 87 K, and diamagnetism measurements indicated 60–70% superconducting phase. Meissner measurements however, in common with most Meissner measurements on Bi-containing superconductors, indicated substantially less superconducting material. Critical currents were comparable to untextured ceramic and flux grown single crystals. Float zone crystallization shows great promise for preparing single crystals and textured ceramics of incongruently melting superconductors, even when detailed phase diagrams are not known.