Preparation and Characterization of Homogeneous YBCO Single Crystals with Doping Level near the SC-AFM Boundary
Ruixing Liang, D.A. Bonn, W.N. Hardy, Janice C. Wynn, K.A. Moler, L. Lu, S. Larochelle, L. Zhou, M. Greven, L. Lurio, and S.G.J. Mochrie
Published in Physica C 383, 1 (2002).
Preprint: Cond-mat/0111379.

High-purity and homogeneous YBa₂Cu₃O_y single crystals with carrier doping level near the AFM-SC boundary have been obtained in the oxygen content range between y = 6.340 and 6.370. The crystals are ortho-II phase at room temperature and undergo the orthorhombic to tetragonal transition at about 140°C. They show sharp superconducting transitions, with T_c between 4 and 20 K. T_c changes by 0.8 K when the oxygen content y is changed by 0.001, and is also sensitive to annealing conditions near room temperature, due to the dependence of doping on oxygen ordering correlation lengths. Crystals with oxygen content y lower than 6.345 are non-superconducting.