Diffusion of Sr in Bi₂Sr₂Ca_n–1Cu_nO_2n+4

Tracer diffusion of ⁸⁵Sr in polycrystalline Bi₂Sr₂Ca_n-1Cu_nO_2n+4 has been investigated for n = 1, 2, and 3 in an oxygen atmosphere between 775 and 850 °C. A radiotracer serial-sectioning technique was used to measure the concentration profiles, which were fit to a solution of the diffusion equation to calculate the diffusivities. The activation energies were 403, 553, and 519 kJ/mole, for n = 1, 2, and 3, respectively. However, the absolute values of D for the various layered superconductors did not differ by more than an order of magnitude over the measured temperature range. The diffusivity of Sr at 800 °C for n = 1 or 2 over an oxygen partial pressure range of 10³ to 10⁵ Pa increased as the pressure decreased.