Improve superconductivity with carbon nanotubes

Physicists from Argentina and the US have just announced that they have significantly improved the superconductivity of MgB2 alloys by doping multi-walled carbon nanotubes.

Adriana Serquis (Centro Atomico Bariloche-Instituto Balseiro) and colleagues at Los Alamos National Laboratory have shown that this doping helps to significantly improve the critical magnetic field and the critical current of the MgB superconducting alloy - Two extremely important parameters for the use of superconducting materials in practice.

Magnesium diboride (MgB2), first discovered to be superconducting in 2001, opens up a wide range of applications for technology due to its high critical temperature (39 K - highest in alloys). Cheap price and simple chemical composition. However, the upper critical magnetic field (the superconducting magnetic field) is only between 14 and 16 T and the critical current also only reaches 2.104 A / cm2 at 5 T. Remember, MgB2 is a type 2 superconductor. , so it has two critical magnetic fields and the upper critical field is the critical value of superconductivity elimination, and the lower critical value (lower) is the critical value that the outer field can penetrate into the material. superconducting We know that, to use superconductors in magnetic coils, superconducting ceramics with high critical temperatures are difficult to use, so this alloy is a great choice.

And recently, Serquis and his colleagues have been successful for the first time while simultaneously optimizing these two parameters by doping into this double -walled carbon nanotubes (DWNTs) nanotubes. High quality MgB2 block samples were made by Mg vapor intrusion method at Centro Atómico Bariloche (Argentina) and then doped the DWNTs tubes, then conduct electrical and magnetic properties with universal devices. as magnetometer . in pulse magnetic field at High Magnetic Laboratory (Los Alamos).

They found that about 3.5% atoms of doped DWNTs can produce optimal properties for MgB2 with a critical current density of up to 5,104 A / cm ² (when the external field is 5 T ) and upper critical magnetic fields up to 44 K (at a temperature of 5 K). Another value is also recorded as the critical magnetic field over 41.9 T at 4 K when the doping content is 10% atoms (see figure). This means that the critical magnetic field is improved up to 3 times while the critical current density is also raised up to 2.5 times. The DWNTs content is precisely determined by analyzing crystal structure by X-ray diffraction method.

According to the team's work, published in the journal Superconductor Science and Technology, No. 20, page L12 , these results can be explained by the two roles of DWNTs in the structure of MgB2:

First , it is partially dissolved nanocarbon tubes into MgB2 matrices, acting as a carbon source that increases the critical magnetic field value to the highest value ever observed.

Second, that portion of the nanocarbon tube retains its structure, acting as a vortex pinning centrifuge in MgB2, thus significantly increasing the critical current density value. This is entirely possible because the tube diameter is similar to the combined length of MgB2 superconductors.

Physicists also argue that this enhancement can be described by one of the theoretical models being used as two-slot superconducting theory, such as MgB2 . And another part is to use this material in practical applications like superconducting magnets. This work could be a way to open up the creation of superconducting coils with large magnetic fields by improving the value from the critical field.

The upcoming plan of the group (Argentina and the US cooperation) is to doping MgB2 with other nanomaterials to improve the properties of the material: "Besides, we will produce the first MgB2 wires for the application. using a DWNTs doping component " - Serquis told Nanotechweb.org.

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