Removing sodium left boron unusually conductive—and able to deform

An Imma-B60 nanopillar from which nearly all sodium had been removed survived about 23% plastic deformation under compression. Instead of behaving only like the extremely hard forms for which boron is better known, this tiny crystal changed shape permanently—and the resulting material also conducted electricity unusually well.

The combination matters because an element’s properties depend not just on which atoms are present, but on how those atoms are arranged. Diamond and graphite, for example, are both carbon. Researchers have now used a temporary atomic scaffold to coax boron into a structure it would not ordinarily adopt, then removed nearly all of that scaffold without making the framework collapse.

In a Nature Chemistry study, the researchers first formed a sodium–boron precursor called Na4B60 under high pressure. They then heated it under vacuum so that sodium escaped from the crystal. The resulting material, Imma-B60, retained an open framework built from 12-atom boron clusters connected by triangular three-atom units.

The construction-scaffold analogy is helpful, provided it is not taken too literally. Sodium was part of the precursor crystal, not simply packing material poured into an existing structure. Its presence helped make that arrangement accessible; removing nearly all of it left open regions inside the boron network.

Three tests, three different claims

No single measurement establishes the entire story. Diffraction, microscopy and composition measurements provided converging support for the proposed structure and for near-complete—not necessarily total—sodium removal.

X-ray diffraction tests a crystal’s repeating atomic arrangement by recording how it scatters X-rays. The reported powder pattern agreed with the proposed Imma-B60 structure and was compared with patterns for other known or predicted boron allotropes. Electron microscopy offered a second view at much smaller scales, while chemical measurements compared the precursor with material treated under different degassing conditions.

Together, those results support the structural identification. They do not establish how well the material carries current or how it responds to force; those questions required separate experiments.

Electrical measurements produced a conductivity of roughly 9 × 10² siemens per metre, or about 900 S/m. The study reports that this is seven orders of magnitude above β-boron. That phrase can obscure the scale: seven orders of magnitude means a factor of ten million. The researchers also measured a narrow bandgap of about 0.2 electronvolts, consistent with charges moving more readily than they do through typical poorly conducting boron.

For the mechanical result, the team made nanoscale pillars and compressed them along one direction. The Imma-B60 pillars underwent about 23% plastic deformation, associated in the study with the movement of crystal defects known as dislocations. A Nature news report highlights the crucial distinction: after deformation, the material did not bounce back to its original form.

Think of the difference between stretching a rubber band and reshaping a paper clip. The rubber band’s response is mostly elastic; release it and it recovers. The paper clip retains much of its altered shape, demonstrating plastic deformation. Imma-B60 showed the second kind of behavior—but only in nanoscale pillars under controlled uniaxial compression. The study did not demonstrate a bulk sheet or wire that can be bent by hand.

The researchers propose that the open framework permits the dislocation slip responsible for this deformation. That is a mechanism supported by their structural analysis and compression observations, not a consequence that can be assumed merely because the crystal contains empty space.

A scaffold strategy with a precedent

The broad method has worked with another element. In 2014, researchers reported an open-framework silicon allotrope made by synthesizing Na4Si24 under pressure and then thermally removing sodium. That silicon study established the precursor-and-degassing strategy as a plausible way to reach structures that ordinary synthesis might miss.

The reported advance here is applying that approach to boron and obtaining this particular combination of an open framework, high conductivity and substantial permanent deformation. It is a materials-making result, not yet a technology demonstration. The researchers did not show a working component, a mass-production process or long-term performance inside a device. What they did show is more foundational: temporary atoms can help boron assemble into a structure whose measured behavior differs dramatically from its familiar forms.