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Figure: Graphite plus distilled water may be a superconductor at room temperature. Source: CHARLES D. WINTERS/SCIENCE PHOTO LIBRARY Can you imagine that a little graphite plus a few drops of distilled water can make a room temperature superconductor that scientists think about? German researchers have announced a breakthrough: a material that can be a superconductor (which can conduct electricity with zero resistance) at room temperature and higher. Superconductors offer enormous potential for energy savings, but to date, this material has only worked at temperatures below about 110 degrees Celsius. Today, Pablo Esquinazi of the University of Leipzig and colleagues report that flaky graphite particles immersed in water seem to be capable of producing superconductivity at temperatures above 100 degrees Celsius. Although Esquinazi admits that the discovery "sounds like science fiction," the research has been published in the peer-reviewed journal Advanced Materials, and other physicists have told Nature that the results are tempted. Sexual, but worthy of further review. Graphite is composed of a layer of carbon atoms arranged in a hexagonal grid, which exhibits superconductivity when doped with an element capable of providing additional free electrons. For example, calcium graphite is superconducting at 11.5 degrees Kelvin (about -260 degrees Celsius), and theorists predict that if there are enough free electrons available, the temperature can rise to 60 degrees Kelvin. Esquinazi's team speculates that high-intensity electrons are formed at the interface between adjacent graphite fragments. Researchers have observed superconductivity at the interface of a man-made type of bulk graphite, called pyrolytic graphite, in excess of 100 degrees Kelvin, and they have thought about it by doping flake graphite powder. Whether the interface can reach a higher temperature. The first dopant that the researchers tried was ordinary water. They are very lucky. The researchers added 100 milligrams of pure graphite powder consisting of hundreds of 1 mm long, tens of nanometers thick flake graphite to 20 ml of distilled water. After stirring the mixture for about 23 hours, they filtered out the graphite powder and dried it overnight at 100 degrees Celsius. The researchers found that after placing them in a magnetic field, each sample will remain slightly magnetized when the magnetic field is removed. According to Esquinazi, this trace of residual magnetization is a signal of superconductivity or ordinary ferromagnetism. To find out if they have the attributes of the former, the researchers analyzed how the magnetization varies with the strength of the applied field and the temperature. The end result is very similar to the first high temperature oxide superconductor discovered in the 1980s. Esquinazi admits that his evidence is tempting, but it is not dripping. First, his research team has been unable to demonstrate the actual conductivity of its samples with zero resistance. In order to do this, the researchers compressed the soaked powder into granules, forcing the particles to make electrical contact, but they found that this would lead to the disappearance of superconducting effects. Moreover, they cannot prove that there is no magnetic field inside the flake graphite - this is a basic feature of superconductors. Moreover, these samples did not lose their apparent superconductivity as the temperature increased. The team reported that they remained superconducting at about 400 degrees Kelvin (equivalent to 130 degrees Celsius) and a simple extrapolation of the data indicated an upper limit of about 1000 degrees Kelvin. Esquinazi said that since he started writing papers, his team has actually observed signs of superconductivity at 500 degrees Kelvin, but at this temperature, heat has begun to degrade the samples and change their magnetic field strength, thus It is difficult to observe the conversion process to a non-superconducting state. Other physicists still question this. Ted Forgan, a condensed matter physicist at the University of Birmingham in the United Kingdom, said that magnetic data at low temperatures "looks very much like a signal from a superconductor," but he is confused by the changes in its properties at higher temperatures. He said that he expects the residual magnetization to decrease significantly at 300 degrees Kelvin unless the "conversion temperature is actually much higher than this temperature." In the meantime, Alexander Gurevich, a theorist at Old Dominion University in Norfolk, Va., warned that some of the high-temperature superconductivity previously claimed was not able to stand up during the detailed review. He said that the magnetic response may be due to impurities introduced during sample processing. But he stressed that if confirmed, this discovery will have a "deep impact."Compact Powder Case,Round Compact Powder Case,Compact Powder Case with Mirror
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