(Hf0.25Zr0.25Sn0.25Ti0.25)O2 high‐entropy ceramics were designed and prepared, and their microwave dielectric characteristics were investigated together with the microstructures. The single‐phase ...structure in space group Pbcn was determined, and the excellent microwave dielectric characteristics were achieved in the present ceramics: εr = 25.6, Qf = 74 600 GHz at 6.5 GHz and τf = −47 ppm/°C. The significant improvement of Qf value was achieved with a prolonged sintering, where the dielectric constant increased slightly while the negative τf decreased in the absolute value at first and then turned to increase. The variation tendency of microwave dielectric characteristics was deeply linked with the microstructure homogeneity, and the introduction of Hf and Sn elements to create the high‐entropy ceramics resulted in the disordered state, and finally led to the improved Qf value. The present work provided an effective approach to achieve enhanced Qf value in microwave dielectric ceramics.
This study utilizes modulation of ionic disorder and electronegativity differences for targeted component design of high-entropy ceramic compositions. A series of novel multicomponent ceramics with ...the general formula (LaGdYSm)x2Ybx1Zr2O7 (x1+4x2 = 2, x1 = 0.6,0.4,0.2,0) were prepared by solid-state reaction. The evolution patterns of their microstructures were analyzed using XRD and TEM, and the anti-sintering ability and thermophysical properties were evaluated. The results confirm that the multicomponent ceramics gradually transform from the coexistence of pyrochlore/fluorite dual-phase structure to pyrochlore structure with the tuning of the size disorder degree. After 50h of exposure to air at 1500 °C, the ceramics retained excellent phase stability. Segregation of La and Yb elements with large differences in radius size occurs, forming a mixture of the La-rich pyrochlore and the Yb-rich fluorite phases. The specimen with the maximum size disorder exhibits the lowest grain growth rate and the greatest thermal insulation properties. Large lattice distortions and sluggish diffusion effects are responsible for the mutual inhibition of grain growth in the two-phase coexistence zone. The thermal insulation properties of the ceramics show well correlated with the degree of the size disorder, further validating the effectiveness of the component design. Meanwhile, the thermal expansion coefficients of prepared ceramic can reach 11.49 × ∼11.58 × 10−6 K−1 at 1000–1100 °C. The customization principles used in this work fill a gap in the compositional design methodology for multicomponent lanthanum zirconate-based high-entropy ceramics. It is essential for developing rare-earth zirconates with tunable thermophysical properties in the area of thermal barrier coatings.
The (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 high-entropy ceramic coating was fabricated by laser cladding in this study. For the continue and dense coating structure, there were pre-treatments including the ...squash presetting of feedstock powders and the deposition of Al2O3-TiO2 coating on steel substrate by atmospheric plasma spray. The XRD technology was conducted for investigating the phase transitions during the fabrication of (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating. The SEM, EDS technologies and nano-indenter were operated for evaluating the microstructure, composition and mechanical properties of the (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating. The results showed that the feedstocks with various structures were successfully transformed into the (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 high-entropy ceramic with rutile structure as well as the formation of intermediate products in similar structures. The (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating had a tight combination with the Al2O3-TiO2 coating and showed a thick and compact structure, which included various dendritic crystal structures composed of segregated Al2O3. The (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating exhibited a high level of hardness (13.58 ± 2.05 GPa) and elastic modulus (275.24 ± 32.26 GPa).
•(Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 high-entropy ceramic coating was firstly prepared.•The coating was fabricated by laser cladding assisted-with squash presetting.•The coating has a dense structure with thickness of 245 μm and porosity of 1.27 %.•The coating exhibits prominent hardness (13.58 GPa) and elastic modulus (275.24 GPa).
High-entropy rare earth zirconates (RE2Zr2O7) have attracted significant research attention for thermal barrier coatings (TBCs) application due to their superior performance. However, currently used ...high-entropy RE2Zr2O7 shows only the modest improvements, thus limiting their overall performance enhancement. Therefore, novel high-entropy RE2Zr2O7 (La0.2Nd0.2Gd0.2Er0.2Yb0.2)2Zr2O7 (HEC) was synthesized in this study by chemical co-precipitation method, which was characterized by dual-phase and significant differences in ionic radius and atomic mass. Compared with single-component RE2Zr2O7 (RE = La, Nd, Gd, Er, and Yb) ceramics, HEC demonstrates significantly superior performance, including higher hardness (11.705 GPa), fracture toughness (1.693 MPa m1/2), and thermal expansion coefficient (11.1926 × 10−6/K, 1400 °C), and lower thermal conductivity (1.33–1.43 W/(m•K), 26–1000 °C). The comprehensive performance improvement can be attributed to the high-entropy effect, dual-phase nature, and significant differences in ionic radius and atomic mass. This study provides valuable insight into the development of high-entropy RE2Zr2O7 and suggests their significant potential in TBCs.
Aluthough High-entropy oxides have the diversity of elements composition and structures, these compounds always maintain a single-phase crystal structure and show excellent physical and chemical ...properties. Inspired by this, we have synthesized high-entropy pyrochlore oxide (LaY) (Zr0·5Ti0·5Ce0.5Hf0.5)O7 with the sol-gel method, which is denoted as HEPO. To begin with, the HEPO samples calcinated at various temperatures were investigated by using a series of technique, such as TG, FT-IR, XRD and electrochemical workstation and the results indicated that 800 °C was the best processing temperature for HEPO. Besides, a super-concentrated sugar-based solution was used as the electrolyte for the HEPO-800 electrodes and increased the electrochemical window to 3V. Moreover, the HEPO-800 electrode also showed the excellent capacitance of 703.3F·g−1 at a current density of 1A·g−1. Consequently, the symmetrical HEPO-800//HEPO-800 supercapacitor device presents a high capacitance of 128.5F·g−1 at a current density of 3A·g−1. In addition, this device exhibits a high energy density of 160.6 Wh·kg−1 at a corresponding power density of 4500W·kg−1 with outstanding cycling life.
In this paper, we demonstrate that Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 (LLZNTH) high-entropy Li-garnet has a fine microstructure and improved mechanical properties compared with Ta-doped Li-garnet ...(Li6.75La3Zr1.75Ta0.25O12, LLZT). The formation, sintering, and electrochemical properties are also studied. The results indicate that the LLZNTH sample has a finer particle size than LLZT after calcination and ball mill. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) regarding the solid-state reaction process indicate that the LLZNTH forms at a lower temperature than LLZT. Both samples can be densified to a relative density up to ∼93–94% at a temperature of 1100 °C, however, they show significantly different sintering and grain growth behaviors. The LLZNTH sample takes 16 h to reach the maximum relative density while the LLZT sample only needs 12 h. LLZNTH sample has a lower grain growth parameter due to the sluggish effects of high-entropy compounds so that it maintains fine microstructures (grain size ∼10 μm) than the LLZT sample (grain size over 100 μm). Due to the fine microstructures, the LLZNTH sample shows both higher flexural strength (84.8 ± 6.9 MPa compared with 47.9 ± 10.1 MPa) and hardness (8.5 ± 0.8 GPa compared with 7.7 ± 0.4 GPa) than the LLZT sample. Ionic conductivity characterizations indicate that the LLZNTH sample shows a moderate conductivity of 4.67 × 10-4 S/cm at room temperature and a low activation energy of 0.25eV.
High-temperature stability, including sintering resistance and phase stability, is critical for thermal barrier coatings (TBCs) applied at ultra-high temperature over 1500 °C. In this work, we ...reported a high-entropy rare-earth zirconate (Y02La0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 (YLNSE) synthesized by solid-state reaction method. X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive spectrometer (EDS) mapping results confirmed that YLNSE formed a single-phase pyrochlore structure with uniform rare earth elements distribution. YLNSE maintained more uniform microstructure, higher porosity retention, lower grain growth rate and better thermomechanical properties during sintering at 1500 °C, as the results of the ordered crystal structure and sluggish diffusion effect, indicating a better sintering resistance than conventional TBC material yttria-stabilized zirconia (YSZ). In addition, YLNSE also demonstrated high coefficient of thermal expansion (CTE, 11.04 × 10-6K-1, 25–1500 °C) and low thermal conductivity (1.95 W m-1 K-1, 1500 °C), as well as good phase stability at 1500 °C. In view of the excellent high-temperature stability of YLNSE, it is a promising candidate for ultra-high temperature TBCs.
To development large-size and complex high-entropy ceramic (HEC) components, the joining of (Ti0.2Zr0.2Nb0.2Ta0.2Cr0.2)C and Nb metal with nickel-based filler alloy was performed. The microstructure ...was characterized by SEM and the phase composition was analyzed by EDS and XRD. The brazing mechanism of the joint was mainly derived from the diffusion of Nb, which formed the NbC reaction layer in the HEC part and the diffusion zone in Nb metal part. The highest shear strength of the brazed joints at 1170 °C/10min was 139 MPa at room temperature and 117 MPa at 800 °C. In addition, the effect of brazing temperature on the microstructure and shear strength was discussed. This work provided a key method to prepare high-temperature resistant complex and large-size HEC components.
•This work provides a feasible method to fabricate large-size and complex HEC component.•The brazing mechanism is ascribed to the diffusion of Nb to form Nb(s,s) diffusion zone and NbC reaction layer.•A maximum shear strength of the joint is 139 MPa at room temperature and 119 MPa at 800 °C.
