Planar defects-induced low thermal conductivity in a superhard material SiB6

Generally materials with low thermal conductivity require weaker interatomic bonding, considered as soft materials. Here we demonstrate that SiB ₆ with planar structural defects shows low thermal conductivity, but uncommonly high strength. Planar defects-induced polycrystalline SiB ₆ (PD-SiB ₆ ) has a relatively large Vickers hardness, which is comparable to those of well-known superhard materials, despite of relatively low thermal conductivity (<10 W m ^-1 K ^-1 at 300 K). Transmission electron microscopy observations confirmed the presence of numerous planar defects, which were thought to contribute to the improvement of hardness. Thanks to the special characteristics of a trade-off relationship between low thermal conductivity and high strength, we believe that PD-SiB ₆ can be used in new strategies of controlling thermal and mechanical properties in various functional materials.