Relationship between Growth, Structure and Superconductivity of Single Crystal YBa 2 Cu 3 O 7-δ

Abstract

The authors study the crystal growth of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} with additives, using ac susceptibility, X-ray diffraction and STM. One specific additive, BaF{sub 2}, dramatically improves both the crystal growth and the superconducting properties. A cluster growth model is proposed to describe the function of the additive. F{sup {minus}} reduces the Al contamination of Cu-O chains, and the orthorhombicity increases. On a nanometer scale, the roughness of the chains decreases markedly. Superconductivity is further enhanced using noncontaminating crucibles. Large single crystals with {Tc} = 93.7 K and {Delta}{Tc} = 0.1 K were grown in Y{sub 2}O{sub 3} or BaZrO{sub 3} crucibles using the BaF{sub 2} additive.