Triclinic rhenium disulphide ($\mathrm{Re}{\mathrm{S}}_2$) is a promising candidate for postsilicon electronics because of its unique optic-electronic properties. The electrical and optical properties of $\mathrm{Re}{\mathrm{S}}_2$ under high pressure, however, remain unclear. Here we present a joint experimental and theoretical study on the structure, electronic, and vibrational properties, and visible-light responses of $\mathrm{Re}{\mathrm{S}}_2$ up to 50 GPa. There is a direct-to-indirect band-gap transition in $1T\text{−}\mathrm{Re}{\mathrm{S}}_2$ under low-pressure regime up to 5 GPa. Upon further compression, $1T\text{−}\mathrm{Re}{\mathrm{S}}_2$ undergoes a structural transition to distorted-$1T^{\prime }$ phase at 7.7 GPa, followed by the isostructural metallization at 38.5 GPa. Both in situ Raman spectrum and electronic structure analysis reveal that interlayer sulfur–sulfur interaction is greatly enhanced during compression, leading to the remarkable modifications on the electronic properties observed in our subsequent experimental measurements, such as band-gap closure and enhanced photoresponsiveness. This study demonstrates the critical role of pressure in tuning materials properties and the potential usage of layered $\mathrm{Re}{\mathrm{S}}_2$ for pressure-responsive optoelectronic applications.

Here, we report the sintering of aggregated submicron cubic boron nitride (sm-cBN) at a pressure of 8 GPa. The sintered cBN compacts exhibit hardness values comparable to that of single crystal diamond, fracture toughness about 5-fold that of cBN single crystal, in combination with a high oxidization temperature. Thus, another way has been demonstrated to improve the mechanical properties of cBN besides reducing the grain size to nano scale. In contrast to other ultrahard compacts with similar hardness, the sm-cBN aggregates are better placed for potential industrial application, as their relative low pressure manufacturing perhaps be easier and cheaper.

Diamond and cubic boron nitride (cBN) as conventional superhard materials have found widespread industrial applications, but both have inherent limitations. Diamond is not suitable for high-speed cutting of ferrous materials due to its poor chemical inertness, while cBN is only about half as hard as diamond. Because of their affinity in structural lattices and covalent bonding character, diamond and cBN could form alloys that can potentially fill the performance gap. However, the idea has never been demonstrated because samples obtained in the previous studies were too small to be tested for their practical performance. Here, we report the synthesis and characterization of transparent bulk diamond-cBN alloy compacts whose diameters (3 mm) are sufficiently large for them to be processed into cutting tools. The testing results show that the diamond-cBN alloy has superior chemical inertness over polycrystalline diamond and higher hardness than single crystal cBN. High-speed cutting tests on hardened steel and granite suggest that diamond-cBN alloy is indeed a universal cutting material.

We report an approach to strengthen micro-grained polycrystalline diamond (MPD) compact through work hardening under high pressure and high temperature, in which both hardness and fracture toughness are simultaneously boosted. Micro-sized diamond powders are treated without any additives under a high pressure of 14 GPa and temperatures ranging from 1000 °C to 2000 °C. It was found that the high pressure and high temperature environments could constrain the brittle feature and cause a severe plastic deformation of starting diamond grains to form a mutual bonded diamond network. The relative density is increased with temperature to nearly fully dense at 1600 °C. The Vickers hardness of the well-prepared MPD bulks at 14 GPa and 1900 °C reaches the top limit of the single crystal diamond of 120 GPa, and the near-metallic fracture toughness of the sample is as high as 18.7 MPa m^1/2.