Transition metal ‘cocktail’ helps make brand new superconductors

2type crystal structure of the newly created superconducting co._0.2Ni_0.1Cu_0.1Rh_0.3Ir_0.3Zr₂ connection, with a HEA-type Tr site. Credit: Tokyo Metropolitan University “width =” 800 “height =” 450 “/>

Researchers from Tokyo Metropolitan University have mixed and designed a new high entropy alloy (HEA) superconductor using extensive data on simple superconducting substances with a specific crystal structure. HEAs are known to retain superconducting properties up to very high pressures. The new superconductor, Co._0.2Ni_0.1Cu_0.1Rh_0.3Ir_0.3Zr₂, has a superconducting transition at 8K, a relatively high temperature for an HEA. The team’s approach can be applied to the discovery of new superconducting materials with specific desired properties.

It is more than a hundred years since the discovery of superconductivity, where certain materials suddenly show minimal resistance to electric currents below a transition temperature. As we explore ways to eliminate power loss, one way to dramatically reduce power transmission losses is a fascinating prospect. But the widespread use of superconductivity is hampered by the demands of existing superconductors, especially the low required temperatures. Scientists need a way to discover new superconducting materials without trial and error of brute force, and tuning key properties.

A team led by associate professor Yoshikazu Mizuguchi at Tokyo Metropolitan University is pioneering work in a ‘discovery platform’ that has led to the design of many new superconducting agents. Their method is based on high entropy alloys (HEAs), where certain sites in simple crystal structures can be occupied by five or more elements. After being applied to heat-resistant materials and medical equipment, it has been found that certain HEAs have superconducting properties with some exceptional properties, in particular maintaining zero resistance under extreme pressure. The team examines material databases and leading research and finds a series of superconducting materials with a common crystal structure but different elements in specific fields. They then mix and design a structure that contains many of the elements; throughout the crystal, the “HEA sites” are occupied by one of the mixed elements (see Figure 1). They have already succeeded in creating high entropy variants of layered bismuth sulfide superconductors and telluride compounds with a sodium chloride crystal structure.

2-type Co_0.2Ni_0.1Cu_0.1Rh_0.3Ir_0.3Zr₂ in magnetic fields of different strengths. (b) Temperature dependence of electronic specific heat C_el/ T. Credit: Tokyo Metropolitan University “/>

In their latest work, they focused on the copper aluminide (CuAl₂) structure. Compounds that combine a transition metal element (Tr) and zirconium (Zr) in TrZr₂ with this structure it is known to be superconducting, where Tr can be Sc, Fe, Co, Ni, Cu, Ga, Rh, Pd, Ta or Ir. The team combined a “cocktail” of these elements using arc fusion to create a new HEA-type compound, Co_0.2Ni_0.1Cu_0.1Rh_0.3Ir_0.3Zr₂, which showed superconducting properties. They looked at resistance and electronically specific heat, the amount of energy the electrons in the material use to raise the temperature, and identified a transition temperature of 8.0K. This is not only relatively high for a HEA-type superconductor, but confirms that the material has the characteristics of ‘large’ superconductivity.

The most exciting aspect of this is the wide variety of other transition metals and ratios that can be tested to envision higher transition temperatures and other desired properties, without altering the underlying crystal structure. The team hopes that their success in the near future will lead to more discoveries of new HEA superconductors.

Provided by Tokyo Metropolitan University