Manganese disulfide is normally a soft insulator. But when it compresses, it suddenly becomes a metal, which is decently electrically conductive. A further increase in pressure leads to the return of the material to the insulator roll. All this happens at normal temperatures and the necessary pressures are not dizzying. A wonderful phenomenon could find practical use, for example in electronics.
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Changes in the arrangement of atoms in manganese disulfide. From left to right there is a higher pressure. The rings are manganese atoms, the eights 2 sulfur atoms. Credit: Dean Smith, Argonne National Lab.
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Compared to non-conductors, metal conductors are usually located on opposite sides of the conductivity spectrum. However, US experts have recently discovered material that can “switch” between a conductor and an insulator, even at room temperature. It is manganese disulfide MnS2, which is normally an insulator, but you just have to push it hard and suddenly it’s a conductor.
Ranga Dias s diamantovou kovadlinou. Kredit: University of Rochester / J. Adam Fenster.
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The conductivity of a material is determined by how easily the electrons move in it. Ranga Dias of the University of Rochester and colleagues studied substances in which conductivity is associated with the pressure to which the substance is exposed. They found such bizarre behavior in manganese disulfide. Under normal circumstances, it is a soft insulator. However, when a small amount of this material was placed in a diamond “anvil” (DAC) and subjected to pressure, it turned into a metallic and conductive material. To make matters worse, as the pressure increases further, the material switches back to the form of an insulator.
Logo. Kredit: University of Rochester.
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As Dias notes with astonishment, metal usually remains metal. It is very unlikely that the metal will turn into an insulator. The behavior of manganese disulfide is exceptional in this respect. When scientists have studied this phenomenon in detail, it has been shown that in the insulator phase, the electrons of the mentioned material are arranged randomly and it is extremely difficult for free electrons to move the material and generate an electric current. When manganese disulfide is compressed, its electrons get closer together and tend to form vapors. Free electrons then move through the material many times more easily and a conductor is formed.
Remarkably, the conditions necessary to change the electrical properties of manganese disulfide are not draconian. It works at a temperature of 27 ° C and at pressures of 3 to 10 GPa. Similar changes in electrical conductivity usually require ultra-low temperatures and pressures in excess of 180 GPa, which is difficult to achieve outside the laboratory. It seems that the special properties of manganese disulfide could find practical use, for example in electronics.
Literature
University of Rochester 26. 7. 2021.
Physical Review Letters 127: 016401.
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