Researchers from the American National Laboratory in Berkeley have discovered a new substance, which, being in a metallic state, conducts electric current well, being at the same time a thermal insulator. This feature of this material can be very useful in some areas, however, it fundamentally breaks all established principles and understanding of how electrical conductors work.
The properties of a substance discovered back in 2017 violate the Wiedemann-Franz law, according to which the thermal conductivity of a conductive material is proportionally dependent on its specific electrical conductivity. It is in accordance with this law that such things as electric heaters, electromagnets and electric motors become warm and even hot during their use.
The detected substance is vanadium dioxide (VO2), a material which, under normal conditions, is a transparent dielectric. But when the temperature rises above 67 degrees Celsius, this material goes into a metallic conductive phase. “The unusual properties of vanadium dioxide destroy all of our ideas from physics textbooks,” the researchers write, “This discovery is of great importance for understanding the behavior of electrons in some materials”.
In order to understand where such bizarre properties come from from vanadium dioxide (thermal conductivity, which is 10 times less than the value determined by the Wiedemann-Franz law), scientists studied how electrons move in the crystal lattice of this material. And the reason for this was the unusual synchronization of the motion of all electrons. “The electrons inside this material move together as a fluid stream, and not as separate particles, which is the case in other metallic substances,” the researchers write, “With this orderly movement, the electrons do not touch the nodes of the crystal lattice, which is the basis of heat transfer in other materials. ”
In their studies, scientists began to introduce various additives in vanadium dioxide and see how this affects the properties of the material. The addition of tungsten made it possible to lower the temperature of the transition of the material to the metallic state and increased its thermal conductivity. This will allow, for example, to create cooling elements that will begin to work only when the temperature of the cooled object exceeds a certain threshold.
In addition to “games” with electrical and thermal conductivity of vanadium dioxide, scientists have found that this material has another unique property – under normal conditions, this material is transparent in all light ranges, but at temperatures above 60 degrees Celsius it begins to reflect infrared light, remaining transparent to visible light. Due to these properties, vanadium dioxide with some additives can be used as a coating for smart windows that can lower the room temperature without the need for air conditioning.
In order to more accurately study the unusual properties of vanadium dioxide and other similar materials, which, no doubt, will be found in the future, scientists will need to conduct a lot of different studies. And these studies will be carried out, taking into account the prospects of creating a number of real commercial technologies, which now exist only in science fiction films and works.
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