Unprecedented high irreversibility magnetic field in a nontoxic cuprate superconductor: a promising superconducting material for the high power application above the liquid nitrogen temperature

November 13 07:15 2018

A very important property for a superconductor is that it can carry non-dissipative superconducting current, so it can produce a huge magnetic field when making the superconductor into a magnet. This property can be applied for medical treatment, controlled nuclear fusion, high-energy accelerator, the new generation of maglev transport, etc, For a superconductor to carry the non-dissipative supercurrent, a boundary, namely, the irreversibility line Hirr(T), is very crucial. This phase line actually separates the phase diagram into zero and finite resistive dissipation. Usually, if a superconductor can carry higher non-dissipative supercurrent with a higher irreversibility magnetic field, it will have a better perspective for applications.

A superconductor goes into a superconducting state below the transition temperature Tc, so a superconductor with higher Tc has better potential applications. The liquid nitrogen is an easily made and low-cost cryogen with boiling temperature of about 77.3 K. It is very crucial for applications if we find superconductors with Tc beyond the liquid nitrogen boiling temperature and high irreversibility magnetic field. In the cuprate family, some compounds of the Y-based [YBa2Cu3O7δ (Y-123), Tc≈90K], Bi-based [Bi2Sr2Ca2Cu3O10+δ (Bi-2223), Tc≈110K], Hg-based [HgBa2Ca3Cu4O10+δ (Hg-1234), Tc≈124K], and Tl-based [Tl2Ba2Ca2Cu3O10+δ (Tl-2223), Tc≈125] systems show superconducting transition temperatures beyond 77K. However, for Hg- and Tl-based systems, the toxic elements Hg and Tl strongly constrain the high-power applications of these materials. The nontoxic Bi-based system also has a transition temperature exceeding 100 K, but the very layered structure and huge anisotropy do not allow a high irreversibility field at the liquid nitrogen temperature: the irreversibility field and superconducting current density decrease rapidly with increasing temperature in the moderate temperature region. The Y-based YBa2Cu3O7δ (YBCO), which is nontoxic and has a high irreversibility field, is thought to be a promising material for applications. But it is extremely difficult to produce long superconducting wire for the short coherent length, it can not realize large-scale applications up to now.

The group of professor Hai-Hu Wen in Department of Physics of Nanjing University successfully synthesized the nontoxic cuprate superconductor (Cu,C)Ba2Ca3Cu4O11+d with Tc=116K under high pressure and high temperature. Systematic resistivity and magnetization measurements show it has the highest irreversibility magnetic field in liquid nitrogen temperature region. This work has been published recently in Science Advances 4, eaau0192 (2018) on September 28, 2018.

Figure 1 shows the temperature-dependent resistivity of sample 1 under different magnetic fields. If a criterion of resistivity of 1%ρn(Tc) is chosen, as marked by the blue horizontal dashed line, the determined irreversibility field is 15 T at about 82K. Actually, even higher values of irreversibility fields are found in another sample. If the weak links between the polycrystalline samples are improved, the irreversibility line may be even higher.

Fig 1. Temperature dependence of resistivity and magnetization of sample 1. (A)

Temperature dependence of resistivity under different magnetic fields from 0 to15 T. The inset shows the temperature dependence of magnetic susceptibility measured in ZFC and FC modes under a magnetic field of 10 Oe. (B) The same data in (A)in the semilogarithmic scale. The blue horizontal dashed line represents the criterion of resistivity 1%ρn(Tc), which is used to determine the irreversibility line.

Figure 2 shows the comparison of the irreversibility lines for our samples and other cuprate systems (including polycrystalline samples, film/single crystal with H//c). From the data, we can see that the irreversibility field of (Cu,C)Ba2Ca3Cu4O11+d is the highest in the temperature region of 77 K to 116 K. We use the highlighted area to indicate the region with finite supercurrent (or zero/weak resistive dissipation) of our sample as compared with YBCO. One can see that there is a large area beyond the irreversibility line of YBCO where the samples can carry non-dissipative supercurrent, providing great potential for applications above the liquid nitrogen temperatures, which may stimulate the research of the cuprate superconductors and eventually lead to large-scale applications.

Fig 2. Irreversibility lines of different cuprate systems.

Irreversibility lines for (Cu,C)-1234 (this work, sample 1 and sample 2), YBCO 1 and YBCO 2 (single crystals, H||c axis), Bi-2223 (thin film, blue down triangles), Bi-2223 (single crystal, cyan diamond), and (Tl,Pb)-1223 (pink triangles). The highlighted area indicates the region for zero dissipation above the boundary of YBCO. The black dashed line shows the trend of the irreversibility line of YBCO with Tc = 91 K.

It should be emphasized that the present samples were made through the high-pressure synthesis. The present results just show very good intrinsic properties for application of the non-toxic material (Cu,C)Ba2Ca3Cu4O11+d and related systems. It is highly desired to try new methods with lower pressure or thin-film deposition to make the superconducting wire/tape based on this promising material.

This work is independently completed by the group of professor Hai-Hu Wen, Ph.D student Yue Zhang is the first author of the paper, professor Hai-Hu Wen and Xiyu Zhu are the corresponding authors.

Article link:http://advances.sciencemag.org/content/advances/4/9/eaau0192.full.pdf

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