High-purity and homogeneous YBa2Cu3Oy 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 Tc between 4 and 20 K. Tc 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.
Bibliographical noteFunding Information:
The Stanford University X-ray group was supported by US Department of Energy under contract nos. DE-FG03-99ER45773 and DE-AC03-76SF00515, and by NSF CAREER Award no. DMR-9985067. Beamline 8-ID at the Advanced Photon Source is supported by the US Department of Energy via Grant DE-FG02-96ER45593.
- Low doping
- Ortho-II phase
- SC-AFM boundary