Axial strain effects of superconducting properties in detwinned RE123 coated conductors.

Transcription

1 8th Workshop on Mechanical and Electromagnetic Properties of Composite Superconductors MEM 2016, March 21st - 23rd, 2016,The Doubletree Hotel, Tallahassee, Florida, USA Axial strain effects of superconducting properties in detwinned RE123 coated conductors. S. Awaji, T. Suzuki*, H. Oguro, K. Chiba, K. Hasegawa, K. Watanabe High Field Laboratory for Superconducting Materials (HFLSM), Institute for Materials Research (IMR), Tohoku University *present address: Kyusu University 1

2 RE123 coated conductors 2 Pole figure IBAD textured buffer layer Buffer layer YBCO Polycrystalline metallic tape Schematic grain structure a-domain a-axis b-domain b-axis Int. (arb unit.) YBCO (103) (103)!-scan Longitudinal direction b-axis a-axis ! (deg)

3 Strain effect in RE123 coated conductors 3 Strain dependence of normalized I c Uniaxial pressure effect on T c Y123 compression tension D C van der Laan et al., Supercond. Sci. Technol. 23 (2010) Y123 compression W H Fietz et al., Supercond. Sci. Technol. 18 (2005) 332 The strain effect of REBCO tapes is complicated because of the coexistence of a- and b-axis domains and the large anisotropy of the strain effect in the ab-plane.

4 De-twinning process (Strain Annealing) c b YBCO a = nm b = nm c = nm b-axis is about 1.8 % longer than a-axis T,P (N) h 1200 Annealing condition (In air) h 0.5 h 0.5 h 0.5 h 0.5 h Furnace cooling 200 SS curve at high temperature Temperature fall Strain released at t a 1000 Stress (MPa) J. Z. Liu, M.D. Lan, P. Klavins and R. N. Shelton, Physics Letters A 144 (1990) Young s modulus T = GPa Strain (%)

5 De-twinning by strain anneal Coexistence of a- and b-axis domains Align of in-plain crystal axis (detwin) latitudinal blue b-axis domain red a-axis domain Anneal under strain longitudinal Transmission XRD (Mo K!) conductor Suzuki et al., IEEE TAS, 25 (2015)

6 Cracks and relationship between internal and external strains 6 J c (77K, sf, 0%) = 2.6 MA/cm 2 for as-received = 0.79 MA/cm 2 for a-axis (//cracks) = MA/cm 2 for b-axis ("cracks) After tensile strain anneal with 1%, the cracks along a- axis appeared. Slope! 0.57 We checked cked the internal strain under external strain.

7 Strain dependence measurements of T c and J c (4-point bending) Compression strain sample CuBe Voltage tap Coated conductor inside compression Tensile strain sample Current read Strain gauge Coated conductor outside tensile Acknowledgment: The strain dependency was measured using the Dr. Nishijima s 4 point bending apparatus

8 8 a-axis b-axis S. Awaji et al., Scientific Reports 5 (2015) 11156

9 External strain dependence of T c 9 W H Fietz et al., Supercond. Sci. Technol. 18 (2005) 332

10 Lattice parameter under the strain 10 Optimum value? Macmanus-Driscoll, J. L. & Wimbush, IEEE TAS. 21, 2495 (2011) Rao et al., Physica C , 9 (1994). S. Awaji et al., Scientific Reports 5 (2015) 11156

11 11 J c / J c (0%) K, 0T J c (77K, sf, 0%) = 2.6 MA/cm 2 for as-received = 0.79 MA/cm 2 for a-axis (//cracks) = MA/cm 2 for b-axis ("cracks) 0.94 as-received A-domain B-domain ! (%) As-received: dome-like a-axis: dome-like but shift a peak position b-axis: almost linear

12 External strain dependence of J c in field 12 J c (! ) / J c (0%) As-received a-axis b-axis SP-(Y, Gd) 0 T 0.5 T 1.0 T 2.0 T 3.0 T 4.0 T 5.0 T c c a-axis SP-(Y, Gd) 0 T 1.0 T 2.0 T 3.0 T b-axis SP-(Y, Gd) 0 T 0.50 T 1.00 T 2.00 T ! (%) ! (%) ! (%)! The strain sensitivities of J c are larger in higher fields.

13 Strain annealing under compressive strain 13 Intensity(arb. unit) (020) as-received 0.25% compression 0.5% detwined compression by! = 1.0% b as-recieved detwined by! = 0.5% b (200) " (deg.)

14 J c properties As-received as-recieved % detwined Compression by! = 1.0% b J c (A/cm 2 ) KJ 10KJ 20K 30K 40K 50K 65K 77.3K B(T) J c (A/cm 2 ) K 10K 20K 30K 40K 50K 65K 77.3K B (T)

15 Conclusion 15 We succeeded in de-twinning of REBCO coated conductors by strain annealing, although cracks formed. Using de-twinned REBCO sample, external strain dependences of T c and J c were investigated.!! Critical temperature! The strain dependencies for the a and b axes obey a power-law but exhibit opposite slopes.! The optimum conditions of the CuO 2 plane in RE123 are a square with a lattice constant of nm to attain a high critical temperature.!! Critical current! The strain dependencies of Jc seem to be similar to those of Tc.! Magnetic field increases the strain sensitivity along both a- and b- axes, altough those are opposite each other.!! The annealing under compressive strain is a promising way for detwinning without cracking.