Determination of Ca diffusion in YBCO films by Secondary Ion Mass Spectroscopy

Ca diffusion was studied in c-axis and a-axis oriented YBCO films by Secondary Ion Mass Spectroscopy (SIMS). The films were grown by pulsed laser deposition (PLD). Ca(NO3)2 solutions were deposited on the film surface and annealed over a large temperature range (300–870 °C) in air. The rate of Ca diffusion was measured to be the same in the c-axis and a-axis oriented films. The activation energy for Ca diffusion in YBCO was measured to be 67±10 kJ/mol. Fast diffusion along the grain boundaries was observed at temperatures below 700 °C with an activation energy of 46±12 kJ/mol. At 300 °C, the grain boundary diffusion coefficient is around 1.7×10−14 cm2 s−1, which is 100 times larger than the corresponding bulk diffusion coefficient.