Comparative study of CSD-grown REBCO films with different rare earth elements: processing windows and T _c

Abstract

REBa 2 Cu 3 O 7−x (REBCO, RE = rare earth) compounds with different single RE elements were grown via TFA-MOD (metal-organic deposition of trifluoroacetates) to clarify their T c values when grown by the same preparation method and their processing windows; here: the crystallisation temperatures at a constant process gas composition (pO 2 , pH 2 O). We focussed on the lanthanides (Ln) Nd, Sm, Gd, Dy, Ho, Er and Yb as substituents for Y in the REBCO phase and investigated their growth behaviour in terms of resulting physical (inductive T c and J c (77 K)) and structural properties (determined by XRD, SEM, TEM). All phases were grown as pristine films on LaAlO 3 and SrTiO 3 and compared to their respective nanocomposites with 12 mol% BaHfO 3 for in-field pinning enhancement.With regard to T c and J c (77 K), the optima of both values shift towards higher growth temperatures for increasing and decreasing RE ion size with respect to yttrium. Highest T c values achieved so far do not show a trend that can solely be related to the RE ionic size. On the contrary, T c,90 values of the LnBCO compounds from Sm to Er range between 94.0 and 95.3 K and are, therefore, significantly larger than the highest values of the average-size non-lanthanide, Y, with T c,90 = 91.5 K. J c,sf values at 77 K seem to plateau between 5 and 6 MA cm −2 from Sm to Er and are again clearly above the maximum values we ever achieved for Y with 4.2 MA cm −2 . REBCO phase formations of the very small Yb and large Nd turned out to be more difficult and require further adjustment of growth parameters. All REBCO phases investigated here show distinct dependences of T c on the lattice parameter c.

(RE)Ba2Cu3O7−δ and the Roeser-Huber Formula

“…All T c -data correspond well to the data obtained on bulk samples; in the case of thin films as discussed in Ref. [38], the correlation is not so straightforward. NdBCO-SS is discussed in Section 3.4 below.…”

“…[73]. This solid solution is also the reason for the difficulties reported in [38] to obtain good quality NdBCO thin films with high T c using the standard conditions as for YBCO.…”

“…The cell parameters for the possible REBCO compounds were investigated in Ref. [38] for thin films. Figure 6 presents their results.…”

“…Several REBCO compounds were also calculated for δ = 0.04 and using the literature data collected in Ref. [38]. Here, it is important to note that the calculated T c increases with decreasing x (increasing RE ionic radius).…”

“…Figure 6.Cell parameters of various REBCO compounds, taken from the ICDD database redrawn from Ref [38]…”