Investigations for the growth of large underdoped Bi2Sr2CaCu2O8+δ single crystals

In order to study superconducting physical properties by neutron scattering technique, the necessity to obtain large and high quality optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212) and underdoped Bi-2212 single crystals is prominent. Three routes have been investigated to reach this goal: synthesis under low oxygen pressure by travelling solvent floating zone technique (TSFZ), TSFZ synthesis of yttrium doped Bi2Sr2Ca1−xYxCu2O8+δ and TSFZ synthesis under air followed by post-annealing treatments. With decreasing p(O2) from ambient pressure to 0.1 atm during the TSFZ growth, the superconducting transition temperature, Tc, transits from 87 K (slightly overdoped) to 93 K. On yttrium doped growth, a systematic study of Bi2 Sr2Ca1−xYxCu2O8+δ, where x=0–0.5, was undertaken to correlate the nominal yttrium composition with the yttrium crystal composition and to control the Tc as a function of yttrium composition. 85 K underdoped Bi-2212 crystals with a size up to 220 mm3 and a 5 K transition width, ΔTc, were obtained by post-annealing under p(O2)=0.1 atm at 450 °C.