Barium silicate and barium aluminate films were studied for use as chemical reaction and diffusion barrier layers
for Y1Ba2CuO7 (YBC) deposited on sapphire and fused silica substrates by the sol-gel technique. Depth profiling by
secondary ion mass spectrometry (SIMS) was used to characterize the abruptness of the interfaces between the barrier
layer and the YBC film as well as the barrier layer and the substrate. We found that barium aluminate films reacted
with fused silica substrates forming a coarse-grained barium silicate phase. Barium silicate, BaSiO3, also reacted with
silica substrates forming a broad, amorphous reaction zone containing some BaSi2O5. Although barium silicate and
barium aluminate deposited on sapphire formed a BaA112O19 phase, they provided a barrier to barium diffusion from
sol-gel deposited YBC. Crystalline barium aluminate grown on c-cut sapphire was the most effective barrier layer for
the growth of YBC films; compositionally uniform YBC films were made similar to that grown on strontium titanate
substrates. These data show that chemically stable, crystalline films are more effective barrier layers than amorphous
films.
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