A new boron allotrope is unusually pliable and is orders of magnitude more conductive than any of the element’s other forms. It was produced by an innovative precursor-based strategy that might enable the discovery of other materials with interesting properties.
The new material was discovered by a team led by Xiao-Ji Weng and Xiang-Feng Zhou from Yanshan University in Qinhuangdao, China. Their method involves first producing sodium boride (Na4B60), before removing the sodium to leave a pure-boron structure called Imma-B60.
Na4B60 was first made in 1970 but is relatively unstudied due to the difficulty in producing high-quality crystals. Weng and Zhou’s team first developed a high-pressure synthesis method to produce larger crystals, which were then ground into a powder. The sodium was removed by applying a vacuum to the material and heating it to 900°C for two days.
The final structure features icosahedral units, each formed of 12 boron atoms, between which are triangular units formed of three boron atoms. The structure also features empty channels where the sodium atoms had previously been. The researchers suggest that this open framework explains the material’s high plasticity – an unusual property when compared with other covalently bonded elemental materials, which are generally very hard.
Imma-B60 was also found to be far more electrically conductive – by six to seven orders of magnitude – than any other boron allotrope.
The researchers suggest that the strategy of degassing templating units from precursor materials could be transferred to many other compounds. They note that this could enable access to many more unconventional framework materials and offers ‘a promising foundation for the design of mechanically resilient, functional inorganic materials’.
