High critical currents in Zr:GdYBCO superconducting tapes processed by multipass MOCVD

Transcription

1 superior performance. powerful technology. High critical currents in Zr:GdYBCO superconducting tapes processed by multipass MOCVD Y. Chen 1, T. Shi 2, A. P. Guevara 2, Y. Yao 2, G. Majkic 2, Y. Zhang 2, Y. Liu 2 and V. Selvamanickam 2 1 SuperPower Inc, Schenectady, NY University of Houston, Houston, TX MS&T 10 October 17-21, 2010 Houston, Texas SuperPower, Inc. is a subsidiary of Royal Philips Electronics N.V.

2 Introduction Multipass deposition has been proven to be effective in growing thick REBCO films with high critical current. In this technique, a thick film is fabricated by growing multiple thinner films one atop each other in distinctive MOCVD runs. This approach enables high tape speed in each run enabling short deposition times as well as the capability to modify process conditions and film composition in each run to achieve improved properties. 2

3 Present work is on four aspects Thickness dependence of Optimum Composition Towards linear thickness dependence of critical current Multipass processed Zr:GYBCO tape with alternating composition to superpose the properties of the individual layers High critical currents in high magnetic field and low temperature 3

4 Scope of work In this work, we choose Gd=Y in the Zr:GdYBCO films because we consider the properties not only at 77K but also at lower temperatures GdBCO show better property at 77K, but is worse than YBCO at lower temperature. On the other hand, the performance of YBCO is poor at 77K In the design of layer structure for the multi-passes, we also hope that the performance is good not only at 77K, but also good at a lower temperature. So, we introduce the layer structure with alternating composition 4

5 Thickness dependence of optimum composition RE-content dependence of Jc for Zr:GYBCO films with thickness of ~0.5mm Gd+Y=1.2 showed the highest Ic(77K, 0T) for the 0.5mm films Jc (MA/cm 2 ) K 0T 1T, //ab 1T, //c 1T, min What is about thicker films? The thickness dependence of optimum composition has not been reported Gd+Y 5

6 With increasing film thickness, the composition optimized for highest Ic(77K, 0T) is shifted to higher RE-content The Zr:GYBCO films with thicknesses of 0.7mm, 1.4mm, 2.1mm and 2.8mm are made in the 4 passes of one experiment. RE = Gd + Y Gd = Y Ba =2 Cu = 3.3 Zr = Conclusion: optimum composition depends on thickness High RE-content could reduce the Ba-Cu-O phase. This benefits the thick films 6

7 Towards linear thickness dependence of Ic This is a 7 pass experiment. The thickness increment in each pass is about 0.5mm The composition of the Zr:GYBCO film is of Gd = Y Ba =2 Cu = 3.3 Zr = Gd+Y content 1.5/1.2 Ic increases linearly with the thickness, till 3 μm. 7

8 Jc (MA/cm 2 ) Multipass processed Zr:GYBCO tape with alternating composition We proved that the 2-dimensional defect structure, horizontal aligned layers and lines comprised of RE 2 O 3 precipitates and vertically aligned BZO columns, could be responsible for the enhancement and suppression of the ab-peak and c-peak B//c B//ab B//ab (Gd,Y)1.1 77K, 1T Angle (degree) Can we combine layers with different properties? Jc (MA/cm 2 ) K, 1T (Gd,Y) Angle (degree) 8

9 Four passes of Zr:GYBCO with alternating GD-& content between 1.5 and 1.2 Zr:GYBCO film made in 4 passes. 0.7μm in each pass. Gd = Y Ba =2 Cu = 3.3 Zr = Gd + Y = 1.5\1.2\1.5\1.2 I c (77K,1T) = 194A/cm-w, Ic(77K,0T) = 961A/cm-w, 2.8μm thick 9

10 Four-pass with alternating Gd+Y content: 1.5 / 1.2 / 1.5 / 1.2 Zr:GYBCO film made in 4 passes Gd = Y Ba =2 Cu = 3.3 Zr = Gd + Y = 1.5 \ 1.2 \ 1.5 \ 1.2 General surface appearance of the 2.8μm thick film: No Ba-Cu-O related island or screw growth was seen 10

11 Four-pass with alternating Gd+Y content: 1.5 / 1.2 / 1.5 / 1.2 Zr:GYBCO film made in 4 passes 2.8μm Gd = Y Ba =2 Cu = 3.3 Zr = Gd + Y = 1.5 \ 1.2 \ 1.5 \ 1.2 Cross sectional TEM shows the layers characterized with high or low RE content 11

12 Four pass with alternating Gd+Y content: 1.5 / 1.2 / 1.5 / 1.2 Layer with Gd + Y = 1.5 Structure dominated with layers of defects. The (Gd,Y) 2 O 3 precipitates forms layers close-spaced parallel to ab-plane 12

13 Four-pass with alternating Gd+Y content: 1.5 / 1.2 / 1.5 / 1.2 Layer with Gd + Y = 1.2 Characterized with 2- dimensional defects BZO columns and RE 2 O 3 layers 13

14 Four-pass with alternating Gd+Y content: 1.5 / 1.2 / 1.5 / 1.2 The transition layer was not able to generate enough random oriented defects Ic(77K,0T) = 961A/cm, Ic(77K,1T) = 194A/cm, Ic(77K,1T//ab)=405A/cm Ic(77K,1T//c) = 267A/cm More complicate layer structures are needed to flat the Ic-angle curve, such as thinner layers in each pass, REBCO/YBCO superlattice. 14

15 Summary Optimum composition varies with film thickness Linear thickness dependence of critical current was achieved for film thickness up to 3mm Multipass processed Zr:GYBCO tape with alternating composition showed high critical currents in self field as well as in 1T magnetic field. Ic(77K,0T) = 961A/cm-w, Ic(77K,1T) = 194A/cm-w, thickness = 2.8mm More complicated layer structures are needed to generate enough random oriented defects Measurement of Ic in high magnetic field and low temperature is on the way 15