In the past 65 years, niobium borate (NBB) has been considered as a high-quality superconducting material. This hypothesis has been detailed in the manuals related to condensed matter and journal physics of scientific papers. At present, scientists from the University of Sao Paulo (USP), the University of Brazil and the State University of San Diego have also started to study this hypothesis.
Recently, an article published in the journal "Physical Review" reported new research results. The research team fully proved that the superconductivity observed earlier did not come entirely from NBB. The superconductivity is the inherent characteristic of the very high-purity niobium wire with "sinuous" NBB grains in the studied samples.
The main participant in this study is Renato de figureiredo Jardim, director of the Lorena Institute of Engineering (eel-usp) and professor of the Institute of physics of the University of Sao Paulo (if-usp). The research was supported by the functional materials research and Development Center (CDMF), one of 17 research innovation and publishing centers (ridc) funded by the research foundation of Sao Paulo (fapesp).
As if-usp professor and eel-usp director, Renato de figureiredo Jardim explained: "it is well known that niobium (NB) has superconductivity when it is cooled at 9.2 Kelvin, that is, very low temperature. Now we have successfully denied the special case of NBB. NBB samples contain a large volume fraction of NBB, and almost no high-purity NB. There are two different crystalline phases in the materials used in the study, and a few phases containing about 98% niobium and 2% boron are superconductors."
By analyzing the electron microscope images selected in the article, the results show that the white filament refers to a few phases, and its composition is 2% boron and 98% niobium. The symbol indicating its composition is nb0.98b0.02, and the gray area with large volume fraction in the figure is NBB.
The researchers pointed out that even if this phenomenon occurs in the small volume fraction of a few phases nb0.98b0.02 with superconducting properties, such content distribution of NBB can create a three-dimensional grid current to move between the ends of the material.
This characteristic may have misled the scientists who first studied and tested NBB, leading them to believe that this material shows superconductivity at a temperature of about 9K.
Jardim believes that the scanning electron microscope provides qualitative evidence for the understanding of NBB lattice structure, that is, the "visual evidence". In addition, Jardim further pointed out: "this evidence alone is not enough to confirm the researcher's hypothesis. We must improve the information and look for quantitative evidence. Based on the data obtained from the research materials, the thermodynamic model is applied to achieve accurate results, and the evidence required by the research is obtained in this way."
Significant contribution of new technology application
Macroscopically, superconductivity is the characteristic of conducting a specific material when it is cooled below a specific temperature, with no energy loss or zero resistance.
At present, researchers can reasonably grasp the application of superconducting technology and realize the technology application in superconducting coils. The cooling and thermal insulation of superconducting coils cause the applied current to flow unsteadily, resulting in the generation of magnetic field, thus avoiding the loss of energy. This superconducting device is widely used in magnetic resonance imaging or MRI equipment.
Jardim pointed out: "in recent years, the superconducting technology has made rapid progress. A special type of vacuum bottle called 'Dewar bottle' is used for low-temperature storage, and its internal temperature can be maintained at the liquid helium level of 4.2 Kelvin (about -270 ° C). These Dewar bottles used to cool superconducting coils can be seen everywhere in the market and are easy to get."
Jardim added: "at present, NBB has not been found to have any technical use, but the 'cousin' of NBB, magnesium diboride (MgB2), has aroused strong scientific interest of scientists in the past 10 years. Our research may contribute to the technical application of MgB2."
Superconductors and diamagnetism
According to yalding, in addition to the above-mentioned macroscopic superconductivity, there is also a macroscopic feature called "perfection". For example, if the material is placed in an external magnetic field, the internal magnetic field of the superconductor will be completely eliminated.
All materials have diamagnetism, but the existence of diamagnetism is not very strong, and it is often easily ignored by other stronger magnetism, such as Ferromagnetism (the material is attracted to the external magnetic field) and paramagnetism (the atomic magnetic dipole of the material is parallel to the external magnetic field through this paramagnetism).
If the diamagnetism should be sufficiently stable like the superconductor, the repulsive force caused by the magnetic field is enough to suspend the material. The research on this kind of material is more and more favored by scientists.
Jardim emphasized: "diamagnetism can be regarded as the current generated on the surface of the material, and the current can generate an induced magnetic field with the same size as the applied external magnetic field and the opposite direction of action, just like the magnetic field immersed in the material is re discharged from the inside."