NANJING UNIV,CTR ADV STUDIES SCI & TECHNOL MICROSTRUCT,NANJING 210093,PEOPLES R CHINA
; INST HIGH ENERGY PHYS,BSRL,BEIJING 100039,PEOPLES R CHINA
; CITY UNIV HONG KONG,DEPT PHYS & MAT SCI,HONG KONG,HONG KONG
Ceramic samples of YBa2(Cu1-yCoy)(3)O(7-)delta with y = 0.00 to 0.08 were synthesized. These samples are free of impurity phases according to X-ray diffraction. The critical temperature T-c decreases with the increase of Co content. The orthorhombic-to-tetragonal transition occurs in the range of 0.02 < y < 0.04. Structural parameters, including the copper-oxygen bond lengths, vary smoothly with y within each phase but exhibit different behavior in the region from orthorhombic to tetragonal phase. These observations are consistent with a model in which superconducting behavior is controlled by charge transfer between the Cu(2)-O-2 sheets and Cu(1)-O chains, which act as reservoirs of charge.