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.

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. 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. 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. 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. Application on 6 GHz niobium Cavities
A15 compounds by
EM-IH technique
6 GHz Nb Cavities

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. Experimental Procedure
Before annealing the samples
(20x10x5) mm
Chemical Treatment
BCP solution:
HF/HNO3/H3PO4 = 1:1:2

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. Heat Treatment
Changing the voltage
and time
Rapid heating, quenching and transformation

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. Binary Compounds
Heat treatment for 10 minutes, changing the temperature from 1500 °C up to 1800 °C

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. 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. 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. Ternary Compounds
Tc= (18±0.35)K
1
Heat treatment for ~1 minute, changing the temperature from 1420 °C up to 2000 °C

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. Ternary Compounds
2
Heat treatment for ~1 minute, changing the temperature from 1420 °C up to 2000 °C

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. (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. Profile temperature vs time
Heating rate:
90 [˚C/s]
Cooling rate:
50 [˚C/s]

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. Results
Microstructure of Nb-Ga-Al_1 sample
Niobium Nb-Al-Ga

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. 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. 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. 6 GHz niobium Cavities

27. Experimental Procedure
Before Coating: 1. Centrifugal Tumbling

28. Experimental Procedure
Before Coating: 2. Chemical Treatment, BCP solution
Before Coating: 3. High Pressure Water Rising

29. Experimental Procedure
Rotator
Liquid Gallium

30. Experimental Procedure
Yttria- stabilized Zirconium oxide
Inside Liq. gallium
or paste with

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. Experimental Procedure

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. Thanks for your attention