Higher pressure ⇒ denser packing ⇒ better superconductivity!

Recently, we had reported the discovery of novel Cu-Bi phases at elevated pressures. Both the Cu11Bi7 and CuBi compounds have unexpected low densities, with one and two dimensional channels running through the materials. We showed that these voids are not completely empty, but provide room for the stereochemically active bismuth lone electron pairs. Such low density structures are however very uncommon in high-pressure phases, and we wanted to know how much pressure is needed to squeeze these bubbles out of the material.

To address this question, we performed a computer experiment by systematically increasing the pressures. We found that the atoms indeed start to move closer together, and eventually form a compound where the atoms are very densely packed in the Cu2Bi phase at above 60 GPa. At these extreme conditions, the Bi lone electron pairs become stereochemically inactive. Simultaneously, the property of this new material changes: the superconducting transition temperature increases from 1.3 K to a value of 2 K! In the near future, experiments will be performed to synthesize this phase and confirm our predictions.

This work was recently published in the new journal Physical Review Materials, and was highlighted as an editors’ choice.

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