Oxygen tracer diffusion in YBa2Cu4O8

Oxygen tracer diffusion has been measured in YBa2Cu4O8 (Y 1:2:4) polycrystals over a temperature range of 400 to 700 degree C in oxygen partial pressures (PO2) that varied between 103 and 105 Pa. Depth profiles were determined by secondary-ion mass spectrometry. The results can be described by an Arrhenius relationship with a pre-exponential of 0.08 cm2/s and an activation energy of 201 kJ/mole. The diffusion coefficient is a strong function of PO2, increasing as PO2 decreases. Oxygen diffuses several orders of magnitude more slowly in Y 1:2:4 than in YBa2Cu3O7-δ Y 1:2:3 with a higher pre-exponential and higher activation energy, and the clear dependence on PO2 indicates that diffusion of oxygen in polycrystalline Y 1:2:4 occurs by a different mechanism than in Y 1:2:3. The results of tracer measurements performed at 600 and 700 degree C on Y 1:2:4 c-axis single crystals indicate that diffusion in the c direction is at least 100 times slower than diffusion in the polycrystals and has a larger activation energy