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Andrea maria camacho romero - preparation of nb3 gaal superconductors


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A15 compounds Nb3Ga, Nb3Al and Nb-Al-Ga have been synthesized on niobium samples by means of induction heating. For the preparation before of treatment, the niobium samples were treated with BCP solution in order to polish the surface. Subsequent, the samples were annealing using an inductor and setup the voltage, time, sample position, temperature, type and pressure of gas used. The inductive measurements indicate that the highest critical temperature was 18 K with DTc 0.35 K, in Nb-Al-Ga#1 sample. Mapping analysis showed the uniform diffusion of aluminium into the niobium. On the contrary, the gallium diffuses creating channels into niobium. The chemical composition was measured by EDS obtaining 82% wt. Niobium, 11.3%wt., Gallium, 4.7% wt., Aluminium and 1.9% wt. Oxygen. Finally, the results indicate that the new technique is feasible for synthesis of A15 superconductor without using a vacuum system.

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Andrea maria camacho romero - preparation of nb3 gaal superconductors

  1. 1. NATIONAL INSTITUTE OF NUCLEAR PHYSICS PADOVA UNIVERSITY Preparation of Nb3(Ga,Al) superconductors by Electromagnetic Induction Heating Camacho A., Rossi A., Palmieri V. Sixth International Workshop on Thin Films and New Ideas for RF Superconductivity
  2. 2. Outline • Introduction of the common techniques used to prepare binary and ternary superconducting A15 compounds. • Electromagnetic Induction Heating Technique. • Experimental procedure: • Samples preparation. • Heat Treatment Performed. • Validation of the technique according superconducting properties and quality of A15 phase on samples. • Application of our technique on 6 GHz niobium cavities. • Conclusions.
  3. 3. Introduction • Common techniques used to prepare A15 superconducting phase: Arc-melting process, chemical vapor deposition (CVD), sputtering, etc. • More specialized techniques such as: • Melt-spin quenching technique: Nb3Ga  20.0K, V3Ga 15.0K, and Nb3Al  18.4K reported by Clemente [1] [1] Clemente,“Superconducting properties of A15 compounds prepared by melt-spin quenching“
  4. 4. EM- Induction Heating  Rapid heating  High temperatures during annealing process (~3000 °C)  Vacuumless  Self-heating of the sample  Short time of treatment  Clean quartz chamber  Economic system
  5. 5. Application on 6 GHz niobium Cavities A15 compounds by EM-IH technique 6 GHz Nb Cavities
  6. 6. EM- Induction Heating System Work head 15 KW Power supply (250-3000)ºC Pyrometer Flange Quartz tube Flange Argon or Helium Low overpressure Exhaust gases Coil Input gas Cavity or Sample
  7. 7. Experimental Procedure Before annealing the samples (20x10x5) mm Chemical Treatment BCP solution: HF/HNO3/H3PO4 = 1:1:2
  8. 8. Experimental Procedure How? • Binary compounds Configuration I:  Liquid Gallium (99.9% pure)  Aluminum Foil (99% pure) • Ternary compounds  Configuration I and II:  Paste: liq. Ga+ Al foil Configuration I Configuration II
  9. 9. Heat Treatment Changing the voltage and time Rapid heating, quenching and transformation
  10. 10. Validation of the EM-IH Technique Materials Number of samples Total Nb-Ga 10 Nb-Al 6 61 Nb-Al-Ga 45 Inductive Measurement Tc
  11. 11. Binary Compounds Heat treatment for 10 minutes, changing the temperature from 1500 °C up to 1800 °C
  12. 12. Binary Compounds • All the Tc are near to 12 K, an average of 3 K above of niobium transition (9 K). • The difficult to synthetize binary A15 compounds (Nb3Ga and Nb3Al) is related to the competition from more stable phases, such as s phases (Nb2Al and Nb5Ga3) and a-Nb phases (solid solution in bcc structure of niobium). • Samples annealed that not reach temperatures higher than 1500ºC, only Nb superconducting transition was evidenced. • The results suggest that the annealing process for 10 minutes at high temperatures degrades the superconducting phase initially formed
  13. 13. Nb3Ga Nb3Al Lattice parameter of 5.1809 Å, very close to the standard lattice parameter, 5.1800 Å Lattice parameter of 5.2141 Å, much higher than the standard value, 5.1780 Å.
  14. 14. From our first attempt of A15 phase, we concluded... 1. Critical temperature results suggest higher diffusion of gallium atoms than aluminum atoms on niobium samples at the same heating conditions (corrosive property of gallium) 2. Wettability problems with liquid gallium which make the preparation of the samples before the heat treatment difficult 3. Very short time of heat treatment is necessary TERNARY COMPOUNDS!!! Nb-Al-Ga
  15. 15. Ternary Compounds Tc= (18±0.35)K 1 Heat treatment for ~1 minute, changing the temperature from 1420 °C up to 2000 °C
  16. 16. High Tc and sharp superconducting transition • Direct transformation of A15 phase from high temperatures of niobium samples. • Ternary compound seems to stabilize the A15 phase.
  17. 17. Ternary Compounds 2 Heat treatment for ~1 minute, changing the temperature from 1420 °C up to 2000 °C
  18. 18. Broad superconducting transitions • Gallium/ aluminum evaporate. • Less control of the stoichiometry. • Further studies are required in order to establish a relation of the quantity of aluminum/ gallium evaporated.
  19. 19. (210) (200) (310) (320) (211) X-ray diffraction in the planes: • (321) Nb3Ga • (110) Nb3Al were not observed Lattice parameter: 5.1904 Å a-Nb3Ga< a-Nb3(Al,Ga)< a-Nb3Al
  20. 20. Profile temperature vs time Heating rate: 90 [˚C/s] Cooling rate: 50 [˚C/s]
  21. 21. Results Microstructure of Nb-Ga-Al_1 sample Niobium x Nb-Al-Ga Niobium Nb-Al-Ga Crack x Element wt% At.% Nb 82±1 66±1 Ga 11,3±0,9 12,1±0,9 O 1,9±0,1 9,0±0,6 Al 4,7±0,2 12,9±0,4 73% at. Nb, 13.3% at. Ga and 14.2% at. Al.  A15 and A2
  22. 22. Results Microstructure of Nb-Ga-Al_1 sample Niobium Nb-Al-Ga
  23. 23. Results Nb-Al-Ga Samples Microstructure of Nb-Ga-Al_1 sample Niobium x x Nb-Al-Ga Niobium Nb-Al-Ga Nb-Al-Ga Niobium
  24. 24. Results Mapping that shows the interface between niobium and superconducting layer Total Counts X-Rays Element Color Smin Smax O K Red 11 99 Ga L Green 17 405 Al K Blue 19 296 Nb L Yellow 151 2805 Ga K Purple 21 366
  25. 25. Nb (L) Ga (K) Al (K) Ga (L)-Nb (L) Al (K)-Nb (L) O (K)- Nb (L) Ga (L)-Al (K) Ga (L)-Al (K)-Nb (L) Ga (L)-Al (K)-Nb (L)- O (K)
  26. 26. 6 GHz niobium Cavities
  27. 27. Experimental Procedure Before Coating: 1. Centrifugal Tumbling
  28. 28. Experimental Procedure Before Coating: 2. Chemical Treatment, BCP solution Before Coating: 3. High Pressure Water Rising
  29. 29. Experimental Procedure Rotator Liquid Gallium
  30. 30. Experimental Procedure Yttria- stabilized Zirconium oxide Inside Liq. gallium or paste with
  31. 31. Cavities Measurements Sample Time [min.] Annealing Temperature, Max. [°C] Notes 1 1,3 2000 Melted 2 14,4 1731 Cavity with a small hole. 3 2,2 1770 Melted 4 3,0 1200 Normal conductor 5 10,0 1091 Normal conductor 6 6,1 2031 Normal conductor 7 1,4 1830 Normal conductor
  32. 32. Experimental Procedure
  33. 33. Conclusions Direct transition of superconducting phase from high temperatures using E-M induction heating. The temperature of the samples are very sensitive by changing voltage and time. Nb+Al+Ga stabilized the A15 superconducting phase. The best configuration is niobium+aluminum/gallium+niobium which avoid the evaporation of gallium and aluminum at high temperatures  more control of the stoichiometry  SHARP HIGH SC TRANSITION
  34. 34. Thanks for your attention