Abstract
We have developed a new preparation method to make Ni-substituted YBa2Cu3O7-delta samples with different distributions of Ni at Cu(1)("chain") and Cu(2)("plane") sites. We found that the high-temperature annealing procedure can change the substitution site of Ni. Ceramic samples of YBa2Cu3-xNixO7-delta (x = 0.00, 0.02, 0.05 and 0.10) prepared in 1-atm oxygen atmosphere were annealed at 800 - 1000 degrees C in various atmospheres with different oxygen partial pressures, and subsequently oxygenated below 550 degrees C. The lower the oxygen partial pressure was, the lower the T-c became. For the samples with the same x, no appreciable difference in lattice parameters and oxygen contents was observed. This result indicates that the distribution of Ni atoms between the chain and plane sites could be altered by the annealing treatment.