Staying Superconductive Under Extreme Pressure

Scientists in China and the US have discovered a metal alloy that superconducts over a wide range of pressures.

AsianScientist (Jan. 23, 2018) – In a study published in the Proceedings of the National Academy of Sciences, a researchers in China and the US have discovered a metal alloy that possesses superconductive properties at a tremendously wide range of pressures.

Superconducters refer to materials that can conduct electricity with zero resistance. Pressure is one of the external variables that can uncover unexpected characteristics in a material. For example, the application of pressure has been known to change the temperature below which a material will superconduct, as well as induce superconductivity in materials that otherwise do not exhibit the phenomenon.

In this study, a team of scientists led by Professor Sun Liling at the Institute of Physics of the Chinese Academy of Sciences (CAS) in Beijing discovered a new material that superconducts over a wide range of pressures. The material is a member of a new family of metal alloys known as high-entropy alloys (HEAs), which are composed of random atomic-scale mixtures of elements from the block of transition metals on the periodic table.

HEAs are interesting in multiple ways, including structurally. They have simple crystal structures, but the metals are arranged randomly on the lattice points, giving each alloy the properties of both a glass and a crystalline material.

The group applied pressure to the HEA using a diamond anvil cell, a device that uses the polished faces of two diamonds to squeeze a sample placed between them. To generate sufficiently high pressure, the size of each diamond’s culet–the ‘point’ at the bottom of the gem–was 40 micrometers, which is about half the diameter of a human hair.

To track the possible structural changes while the sample was in the diamond anvil cell, the group used synchrotron-based X-ray diffraction (XRD) at the Shanghai Synchrotron Radiation Facility. XRD allows researchers to gain structural information on a crystalline sample based on the pattern the X-rays make after they diffract away from the atoms in the sample. They combined these techniques with complementary measurements of resistivity and magnetoresistance to characterize the superconductivity.

The researchers demonstrated that the HEA retains its basic crystal structure, despite the sample’s volume being compressed by up to 28 percent. Even then, the HEA exhibited superconductive properties.

The researchers attribute the material’s unique behavior and stability to its strong crystal structure, combined with the seemingly robust nature of its electronic structure when subjected to a very large amount of lattice compression.

“We have observed that this HEA remains in a state of zero electrical resistance all the way from one-bar of pressure to the pressure of the Earth’s outer core, without structural changes,” said Sun.

“This is a remarkable thing—we know of no other similar material—and it makes this HEA a promising candidate for new applications of superconductors under extreme conditions,” said Professor Robert Cava, who is a senior author of the paper.

The article can be found at: Guo et al. (2017) Robust Zero Resistance in a Superconducting High-Entropy Alloy at Pressures up to 190 GPa.


Source: Chinese Academy of Sciences; Photo: Pixabay.
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