Examination of through-thickness/through-time phase evolution during an MOD-type REBCO precursor conversion using Raman microscopy

Through-thickness/through-time composition analyses were made on REBa2Cu3O6+x (REBCO) films prepared from metal-organic deposited (MOD) precursors on a RABiTS (rolling-assisted biaxially textured substrate) template. Y Dy0.5Ba2Cu3O6+x films were fabricated either by a single precursor coating or by two separate, equivalent precursor coatings with an intermediate decomposition. Specimens were quenched at selected times along a heat treatment profile that simulated conditions used by American Superconductor, then examined by Raman microscopy along mechanically milled slopes through the REBCO films. Upon reaching the reaction temperature TR, the precursor initially transforms into a (Y, Dy)2Cu2O5, CuO, Cu2O, and RE-Ba-F-O phase mix, and this is followed shortly by substrate level REBCO formation that propagates upwards through time. Our results indicate that (1) the single layer (SL) and double layer (DL) films (both ∼ 1.2 μm thick) react to completion at about the same rate and arrive at a similar final composition and (2) some residual Ba-Cu-O phases persist near the top of the fully reacted films. The performance of the SL film was moderately better than that of the DL film, seemingly due to better through-thickness REBCO texture as determined using x-ray diffraction.