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Herein, we report transparent LaGdZr2O7 nano-grained ceramics with an average grain size of 10 nm prepared using the high-pressure sintering method at 5.0 GPa/450 °C. These ceramics showed improved plastic deformation as compared to transparent micro-grained LaGdZr2O7 ceramics. Moreover, the fracture toughness of the nano-grained ceramics reached up to 3.4 MPam1/2, which is 79 % higher than that of the micro-grained samples. This improvement in the fracture toughness of the nano-grained ceramics was associated with the presence of a large number of weak grain boundaries in them.

Tantalum diboride (TaB2) is an important transition metal (TM) diboride that has attracted considerable scientific and industrial interest. Herein, we fabricated TaB2 ceramic samples by combining high-pressure sintering with high-energy ball milling (HEBM) and investigated their microstructure and mechanical properties under high pressure at different sintering temperatures; these results were also compared with those of the bulk TaB2 ceramic. Thus, we evaluated the Vickers hardness, fracture toughness, Young's modulus, and relative density of our TaB2 ceramic at 1200 °C, under 5.5 GPa, to be 26 GPa, 3.8 MPa m1/2, 402 GPa, and 95.11%, respectively. Furthermore, we observed that the Vickers hardness, thermal stability, and fracture toughness are critically controlled with grain size and microstructures of the samples. These observations provide not only useful insights into the physical properties of TaB2 under high pressure and temperatures, but also avenues for the synthesis and design of novel functional ceramics.

Oxide-based near infrared (IR)-shielding coatings consisting of quarter‐wave stacks of oxygen-deficient tantalum oxide (Ta2O5−x) and silicon oxide (SiO2) multilayers and tin-doped indium oxide (In2O3) (ITO) films with the thicknesses of 200–600 nm can block the passage of IR-A (wavelength: 760–1400 nm) and IR-B (wavelength: 1400–3000 nm) radiation, respectively. In this study, the optical properties and microstructure of these oxide-based IR-shielding coatings were investigated. Transmission electron microscopy images indicated that amorphous Ta2O5−x/amorphous SiO2 multilayers were uniform and dense. ITO films were found to be highly crystalline and show carrier concentrations of up to 7.1 × 1020 cm−3, resulting in the strong IR-B optical absorption due to the plasma excitation of the free carriers. Oxide-based IR-shielding coatings with an ITO thickness of 420 nm were found to have near-IR shielding rates of >90% and an average visible light transmittance of >70%. The effects of IR on human keratinocytes were studied to evaluate the IR-induced photoaging in human skin. It was found that the downregulation of cellular proliferation and the enhancement of senescence-associated β-galactosidase activity induced by IR irradiation were significantly inhibited by oxide-based IR-shielding coatings. Thus, this study provides a facile method for the development of coatings for smart windows with high IR-shielding ability and high visible light transmittance.

Studying the mechanical and thermal properties as well as the relationship between microstructure evolution and strengthening mechanisms is crucial for obtaining superior high-temperature refractory molybdenum disilicide-silicon carbide composites. In this study, molybdenum disilicide and silicon carbide powders with different volume ratios were used to fabricate molybdenum disilicide-silicon carbide composites via high pressure and high temperature at 5.5 GPa/1773 K. The introduction of the second phase improved the materials' mechanical properties. Transmission electron microscopy demonstrated that severe plastic deformation generated numerous micro-defects and grain refinement during the high pressure sintering process. The second phase enhancement also improved the samples’ performances. Under high pressure and high temperature sintering process, the thermal and mechanical properties of the materials increased dramatically, including a well Vickers hardness (~20.6 GPa), fracture toughness (~10.3 MPa·m1/2) and thermal stability (>1673 K).

Cubic boron nitride (cBN), a typical superhard material, has garnered significant interest for both fundamental scientific research and technical applications. Here, nanostructured cBN with high-density nanotwins and stacking faults was synthesized by rapid quenching using hexagonal boron nitride (hBN) as the starting material at a moderate temperature (2200 K) and low pressure (13 GPa). This synthetic nanostructured cBN exhibits high Vickers hardness (78 GPa), high fracture toughness (11.8 MPa·m1/2), and extremely high oxidization temperature (1565 K). We propose that the refined grain structure and excellent mechanical properties of the cBN synthesized in this study is attributed mainly to dislocation slips and (111) mechanical nanotwins that dominate this phase transformation.

A series of pure HfB2 ceramics have been prepared by sintering nano-grained powder using high-energy ball milling at 700–1600 °C and 5.5 GPa. The HfB2 ceramics are characterized via various techniques for their residual stress, grain size, density, microstructures and defects, hardness, fracture toughness, thermal stability, and oxidation resistance. All properties strongly depend on the treatment temperature, but the exact manner of dependence for each property varies. The results identified that the HfB2 ceramic sintered at a relatively low temperature of 1000 °C and 5.5 GPa – a bulk pure nano-grained composite for the first time – has the best overall performance. It has a relative density of 99.6%, a Vickers hardness of 26 GPa, a fracture toughness of 5.2 MPa m1/2, and excellent thermal stability and oxidation resistance at high temperatures. Additional strengthening and stabilizing effects are provided by microstructures and defects such as large-angle grain boundaries, stacking faults and twinning. Simultaneous high temperature and high pressure is an effective sintering route for HfB2 ceramics with grain-size ranging from nanometer to micron.

ZnO co-doped with Al and H (HAZO) films were exposed to H/Ar plasma for various durations (0–60 min) at 400 °C to study the effects of heat treatment in H/Ar plasma on the stability of the electro-optical properties and microstructure variations of the films. The crystallite size of the films slightly decreased from 29.6 nm to 26.3 nm when the H/Ar plasma treatment duration (Ta) was increased from 0 min to 30 min at 400 °C, and then decreased significantly to 13.8 nm when the duration was further increased to 60 min. The X-ray photoelectron spectroscopy spectra reveal a dramatic increase in the amount of oxygen-deficient regions and zinc interstitials for Ta values larger than 30 min. Transmission electron microscopy images show high-density basal-plane stacking faults (BSFs) in the films obtained with a Ta of 60 min at 400 °C. The secondary ion mass spectroscopy depth profiles show that the H concentration slightly decreased with increasing Ta up to 30 min. H was significantly out-diffused, enhanced by BSFs and grain boundaries, for Ta values larger than 30 min. The incorporation of H into oxygen vacancies suppressed the defect-induced vibration mode and the passivation of defect states in the as-deposited film; however, this passivation effect was gradually eliminated with increasing Ta. The resistivity of the films remained stable in the range of 5.8×10−4 Ω cm to 6.5×10−4 Ω cm as Ta was increased from 0 min to 30 min, and then increased with further increases in Ta. The electrical properties deteriorated due to a decrease in the crystallite size, high-density BSFs, and the out-diffusion of hydrogen. The figure of merit (ΦTC) was used to evaluate the performance of the electro-optical properties. The ΦTC decreased slightly from 3.32×10−2 Ω−1 to 1.61×10−2 Ω−1 when Ta was increased from 0 min to 30 min, and then decreased dramatically to 5.7×10−3 Ω−1 when Ta was 60 min.

TiC/diamond-like carbon (DLC) nanocomposite films were deposited via steered cathodic arc deposition with various C 2 H 2 flow rates ( f C 2 H 2 ) to study the relationship among the molar fraction of DLC ([DLC]) and the structural, mechanical, and tribological properties of the films. The X-ray diffraction results indicate that the crystallite size of TiC decreased from 14.1 to 3.2 nm when f C 2 H 2 was increased from 60 to 151 sccm. Transmission electron microscopy images show that an elongated TiC grain shape appeared at low f C 2 H 2 values ( f C 2 H 2 was increased from 80 to 100 sccm. Furthermore, the structure of film became a nano-dot TiC/DLC superlattice when f C 2 H 2 was increased to 151 sccm. Rockwell-C indentation tester results indicate that the Ti–TiN–TiC/DLC nanocomposite layer structure had good adhesion between the substrate and films. The hardness increased from 32.5 to 39.3 GPa when f C 2 H 2 was increased from 60 to 80 sccm, and then decreased to 25.1 GPa when f C 2 H 2 was further increased to 151 sccm. The initial increase in hardness was due to grain refinement leading to suppressed multiplication and mobility of dislocations and the subsequent decrease in hardness was due to grain boundary sliding. The toughness was enhanced by the formation of the nanodot TiC/DLC superlattice, as indicated by plasticity calculated from nanoindentation measurements. The friction coefficient decreased from 0.13 to 0.05 with increasing [DLC].