Ultra-incompressible High-Entropy Diborides

Abstract

Transition metal borides are commonly hard and incompressible, offering great opportunities for advanced applications under extreme conditions. Recent studies show that the hardness of high-entropy borides may exceed that of their constituent simple borides due to the "cocktail effect". However, how high-entropy borides deform elastically remains largely unknown. Here, we show that two newly synthesized high-entropy diborides are ultraincompressible, attaining ∼90% of the incompressibility of single-crystalline diamond and exhibiting a 50−60% enhancement over the density functional theory predictions. This unusual behavior is attributed to a Hall−Petch-like effect resulting from nanosizing under high pressure, which increases the bulk moduli through dynamic dislocation interactions and creation of stacking faults. The exceptionally low compressibility, together with their high phase stabilities, high hardness, and high electric conductance, renders them promising candidates for electromechanics and microelectronic devices that demand strong resistance to environmental impacts, in addition to traditional grinding and abrading.

Metallization and Superconductivity in the van der Waals Compound CuP2Se through Pressure-Tuning of the Interlayer Coupling

“…It is interesting to note that the T c of CuP 2 Se is higher in decompression (Figure c) than in compression at the same pressure. We attribute this to the increase in the bulk modulus of nanosized CuP 2 Se due to the Hall–Petch-like effect. ,, Although there is an Anderson limit of the nanoparticle size (possibly ∼5 nm) below which the superconducting transition is prohibited, , the applied high pressure might have a counter effect on the Anderson limit so that the superconductive state of CuP 2 Se nanoparticles was preserved and even enhanced in the decompression.…”

“…At high pressure, the layers of vdW crystals may slide with respect to each other due to the presence of shear stress, leading to cleavage of the crystals and formation of laminates. At high pressure, crystals may also be pulverized to form nanocrystals, as observed in TiO 2 -II, 60 high-entropy diborides, 61 and Lcystine. 62 The electron microscopy images of two CuP 2 Se samples quenched from ∼27 and 52 GPa (Figure 7) indeed show features of layer sliding (Figure S11) that formed lots of sample laminates (Figure 7c).…”

A super‐hard high entropy boride containing Hf, Mo, Ti, V, and W

“…However, the contribution of these regions is small and does not affect microhardness because the indent sizes are smaller than the grain sizes. 1 Examples of the selected indents for the optimized sample are shown in the Supporting Information, Figure S5. From previous investigations, an HEB containing Mo and W had the highest hardness among all of the other HEBs that were reported, 5,8,12,19 indicating that incorporation of Mo and W into HEBs has a hardening effect.…”

“…Transition metal (TM) borides have ultra-high melting temperatures, high hardness values, and outstanding chemical resistance. 1,2 They are metallic electrical conductors and can have thermal conductivity values of more than 100 W/m•K. 3 Due to these properties, they are good candidates for cutting tools, nuclear power generation, wear-resistant parts, microelectronics, and thermal protection materials for atmospheric re-entry vehicles.…”

Coexistence of Superhardness and Metal-Like Electrical Conductivity in High-Entropy Dodecaboride Composite with Atomic-Scale Interlocks

“…The development of high-performance conducting materials with superb hardness is vital for a wide range of advanced applications, from anvils of a large volume press to electromechanical and microelectronic devices under working conditions of high stress. − However, high electrical conductivity is often one of the hallmark attributes of metals arising from the itinerant nature of metallic bonds. Such delocalized metallic bonds allow for transient bond breaking and dislocation formation, and thus, the metals are very soft.…”