Ceramic materials have obvious advantages in thermal stability, but impedance mismatch limited their ability to attenuate electromagnetic (EM) waves. Herein, a novel series of high-entropy (V_0.2Nb_0.2Zr_0.2Ta_0.2X_0.2)B₂ (X=Mo, Ti, Hf) ceramics were successfully and rapidly synthesized using the ultrafast high-temperature sintering (UHS) method based on joule heating. The results indicated that the effect of high-entropy component control on the magnetic loss of the system was relatively small, but the effect on the dielectric loss was larger. Among them, the HEB-Ti sample demonstrated superior absorbing properties, attributed to its relatively moderate dielectric loss and optimal EM impedance matching. At the same time, because of its relatively moderate attenuation constant, it can achieve the maximum penetration of EM wave and the minimum reflection after absorbing wave. As a result, the minimum reflection loss (RL_min) was as low as –40.7 dB, and the effective absorption band covered the entire low frequency range from 2 to 8 GHz. Its excellent absorption performance was mainly due to the synergistic effect of various dielectric attenuation mechanisms, including defect polarization, dipole polarization, and conduction loss. Furthermore, thermogravimetric (TG) analysis showed that the sample exhibited excellent thermal stability and could withstand up to 550 °C in air and up to 1000 °C in argon gas environment. The relevant work provided meaningful references for the design of new high-performance ceramic wave-absorbing materials.

Nano-crystalline diamond has been extensively researched and applied in the fields of tribology, optics, quantum information and biomedicine. In virtue of its hardness, the highest in natural materials, diamond outperforms the other materials in terms of wear resistance. Compared to traditional single-crystalline and poly-crystalline diamonds, nano-crystalline diamond consists of disordered grains and thus possesses good toughness and self-sharpening. These merits render nano-crystalline diamonds to have great potential in tribology. Moreover, the re-nucleation of nano-crystalline diamond during preparation is beneficial to decreasing surface roughness due to its ultrafine grain size. Nano-crystalline diamond coatings can have a friction coefficient as low as single-crystal diamonds. This article briefly introduces the approaches to preparing nano-crystalline diamond materials and summarizes their applications in the field of tribology. Firstly, nano-crystalline diamond powders can be used as additives in both oil- and water-based lubricants to significantly enhance their anti-wear property. Nano-crystalline diamond coatings can also act as self-lubricating films when they are deposited on different substrates, exhibiting excellent performance in friction reduction and wear resistance. In addition, the research works related to the tribological applications of nano-crystalline diamond composites have also been reviewed in this paper.

Bulk diamonds show great potential for optical applications such as for use in infrared (IR) windows and temperature sensors. The development of optical-grade bulk diamond synthesis techniques has facilitated its extreme applications. Here, two kinds of bulk single-crystal diamonds, a high-pressure and high-temperature (HPHT) diamond and a chemical vapor deposition (CVD) diamond, were evaluated by Raman spectroscopy and Fourier Transform Infra-Red (FTIR) spectroscopy at a range of temperatures from 80 to 1200 K. The results showed that there was no obvious difference between the HPHT diamond and the CVD diamond in terms of XRD and Raman spectroscopy at 300–1200 K. The measured nitrogen content was ~270 and ~0.89 ppm for the HPHT diamond and the CVD diamond, respectively. The moderate nitrogen impurities did not significantly affect the temperature dependence of Raman spectra for temperature-sensing applications. However, the nitrogen impurities greatly influence FTIR spectroscopy and optical transmittance. The CVD diamond showed higher transmittance, up to 71% with only a ~6% drop at temperatures as high as 873 K. This study shows that CVD bulk diamonds can be used for IR windows under harsh environments.

Diamond films prepared by chemical vapor deposition will exhibit different surface morphologies, which are determined by the texture and the structural perfection of the deposited diamond. In general, its surface morphology can be controlled by adjusting the deposition conditions. In the present work, textured diamond film was deposited on single crystalline silicon through pre-seeding by diamond nanosheets, rather than controlling the deposition conditions. The employed diamond nano-sheets were prepared by cleavage along a plane, exhibiting good crystallinity. Before chemical vapor deposition, the as-prepared diamond nano-sheets were pre-seeded on the surface of single crystalline silicon as nucleation sites for diamond growth. SEM and XRD results show that the prepared diamond films have a texture. FIB observation reveals that diamonds homogeneously grow on the pre-seeded diamond nano-sheets during chemical vapor deposition, achieving the diamond film with texture. Our work provides a new strategy to prepare textured diamond film.