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Ultrahard Diboride Superconducts Under Pressure

High pressure
Figure 1. At high pressures, the parent structure of tungsten diboride (left) develops a series of defects (right). The defects promote enhanced layering of the tungsten and boron planes, which leads to superconducting behavior.

A unique combination of high-pressure structural studies and transport experiments, together with structure simulations, has led to the discovery that the ultrahard boride WB2 becomes a superconductor under pressure.

Ultrahard materials exhibiting high temperature superconductivity could have many important technological applications, including the fabrication of wear resistant abrasive devices, micro-electro-mechanical systems, and power engineering. Two decades of research on possible high Tc superconductors in members of the diboride family of compounds other than MgB2, however, have not resulted in any materials exhibiting high Tc superconductivity.  Now, a CDAC collaboration including the UIC group, the groups of James Hamlin at the University of Florida, and former CDAC partner Yogesh Vohra at the University of Alabama-Birmingham, and the HPCAT team at the Advanced Photon Source, reports that superconductivity emerges in ultrahard WB2 at extreme conditions.

The abrupt appearance of superconductivity at 55 GPa (with a maximum Tc of 17 K at 91 GPa) does not coincide with any drastic structural change but instead is associated with the formation and percolation of mechanically induced stacking faults and twin boundaries in the parent structure under plastic deformation (Fig. 1). This unprecedented creation of superconductivity through mechanically induced metastable defects opens up new opportunities to search for other materials systems in which metastable structures can be stabilized in the form of planar defects. The use of extreme conditions therefore provides a new route for designing ultrahard superconductors at ambient pressure through defect microstructures that result in novel material properties.

Lim, A. C. Hire, Y. Quan, J. S. Kim, S. R. Xie, S. Sinha, R. S. Kumar, D. Popov, C. Park, R. J. Hemley, Y. K. Vohra, J. J. Hamlin, R. G. Hennig, P. J. Hirschfeld, and G. R. Stewart, Creating superconductivity in WB2 through pressure-induced metastable planar defects. Nature Communications 13, 7901 (2022).