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1.
《Ceramics International》2023,49(12):20398-20405
A dielectric high-entropy ceramic with a composition of Pb(Zr0.25Ti0.25Sn0.25Hf0.25)O3 was designed through B-site doping, and then prepared by solid phase reaction method combined with conventional sintering in air for 3 h at 1200 °C, 1250 °C and 1300 °C, respectively. All the high-entropy ceramics of Pb(Zr0.25Ti0.25Sn0.25Hf0.25)O3 possess a perovskite structure with uniform elemental distribution and their average grain size falls within the range of 3.19–5.5 μm. For the sample sintered at 1250 °C, the dielectric loss is less than 0.07 in the testing frequency of 1 kHz∼1 MHz in 30–350 °C, and the dielectric constant reaches a peak of 14356 at about 270 °C at 1 kHz. At room temperature, the remnant polarization Pr reaches 28.8 μC/cm2. The results demonstrate that the high-entropy ceramic of Pb(Zr0.25Ti0.25Sn0.25Hf0.25)O3 has great potentials in the dielectric and ferroelectric field.  相似文献   

2.
Five equimolar multicomponent oxides were synthesized by replacing one of five cations in (Ce0.2Zr0.2Ti0.2Sn0.2Hf0.2)O2 with Ca2+. The results reveal that except for the one in which Ce4+ replaced by Ca2+, the other four components can form single-phase high-entropy fluorite oxides (HEFOs) at different temperatures, which indicates that Ce4+ is very important for the formation of single-phase HEFOs. The sintering behavior, lattice parameter and properties containing density, porosity, flexural strength and thermal conductivity of the four single-phase HEFOs were investigated. With the change of substituted ions, grain size, relative density, flexural strength and thermal conductivity of the materials vary greatly, which are correlated to the size disorder and mass disorder of these materials. The results of this paper provide a reference for the composition designing and performance tailoring of equimolar HEFOs.  相似文献   

3.
Novel non-equimolar high-entropy SrLa(Al0.25Zn0.125Mg0.125Ti0.25Ga0.25)O4 (SLAZMTG) ceramics with a layered perovskite structure have been prepared via the standard solid-state reaction method. The high-entropy composition belongs to the tetrahedral structure with a space group of I4/mmm, which is confirmed by the XRD and TEM analyses. Excellent microwave dielectric properties with a suitable dielectric constant (εr = 22.5), high quality factor (Qf = 83,003 GHz), and near-zero τf value of −1.7 ppm/°C are obtained in SLAZMTG ceramics sintered at 1400 °C. Meanwhile, a significant enhancement in compressive strength was achieved due to the improvement of configuration entropy, 912 MPa for SLAZMTG compared to 578 MPa in the pure SrLaAlO4 composition. Additionally, the high-entropy engineering in the present work suggests great potential in achieving low thermal conductivities. SLAZMTG ceramics exhibit low thermal conductivities ranging from 2.86 W/m•K at 323 K to 1.99 W/m•K at 673 K, much lower than those of SrLaAlO4 and other perovskite ceramics.  相似文献   

4.
《Ceramics International》2022,48(7):9602-9609
The (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xTix)2O7 (x = 0–0.5) high-entropy ceramics were successfully prepared by a solid state reaction method and their structures and thermo-physical properties were investigated. It was found that the high-entropy ceramics demonstrate pure pyrochlore phase with the composition of x = 0.1–0.5, while (La0.2Gd0.2Y0.2Yb0.2Er0.2)2Zr2O7 shows the defective fluorite structure. The sintered high-entropy ceramics are dense and the grain boundaries are clean. The grain size of high-entropy ceramics increases with the Ti4+ content. The average thermal expansion coefficients of the (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xTix)2O7 high-entropy ceramics range from 10.65 × 10?6 K?1 to 10.84 × 10?6 K?1. Importantly, the substitution of Zr4+ with Ti4+ resulted in a remarkable decrease in thermal conductivity of (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xTix)2O7 high-entropy ceramics. It reduced from 1.66 W m?1 K?1 to 1.20 W m?1 K?1, which should be ascribed to the synergistic effects of mass disorder, size disorder, mixed configuration entropy value and rattlers.  相似文献   

5.
《Ceramics International》2022,48(8):11124-11133
A series of rare-earth-tantalate high-entropy ceramics ((5RE0.2)Ta3O9, where RE = five elements chosen from La, Ce, Nd, Sm, Eu and Gd) were prepared by conventional sintering in air at 1500 °C for 10 h. The (5RE0.2)Ta3O9 high-entropy ceramics exhibit an orthogonal structure and sluggish grain growth. No phase transition occurs in the test temperature of 25–1200 °C. The thermal conductivities of all (5RE0.2)Ta3O9 ceramics are in the range of 1.14–1.98 W m?1 K?1 at a test temperature of 25–500 °C, approximately half of that of YSZ. The sample of (Gd0.2Ce0.2Nd0.2Sm0.2Eu0.2)Ta3O9 exhibits a low glass-like thermal conductivity with a value of 1.14 W m?1 K?1 at 25 °C. The thermal expansion coefficient of (5RE0.2)Ta3O9 ceramics ranges from 5.6 × 10?6 to 7.8 × 10?6 K?1 at 25–800 °C, and their fracture toughness is high (3.09–6.78 MPa·m1/2). The results above show that (5RE0.2)Ta3O9 ceramics could be a promising candidate for thermal barrier coatings.  相似文献   

6.
《Ceramics International》2021,47(21):29960-29968
Here, we report a novel high-entropy rare earth zirconate (HE-REZ) (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2Zr2O7 ceramic aerogel prepared through a sol-gel template method and high-temperature calcination followed by 3-D-structure reconstruction. The structural evolution and crystallisation behaviour of the prepared aerogel were characterised through scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results indicated that the as-prepared HE-REZ ceramic aerogels had a typical nanoporous structure. The HE-REZ ceramic aerogels thermally treated at 900 °C presented an ultralow room temperature thermal conductivity of 0.031 W/(m·K), high specific surface areas of 443.26 m2/g and a relatively high strength of 12.95 MPa. The effects of different calcination temperatures on the microstructure of the samples were also investigated. Therefore, the excellent insulation performance of these unique HE-REZ ceramic aerogels indicate that they can be used as high-temperature insulators for hypersonic vehicles in the future.  相似文献   

7.
A new high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B2 was designed to investigate the effect of introducing rare-earth metal diboride ScB2 into high-entropy diborides on its structure and properties. The local mixing enthalpy predicts that (Hf0.25Zr0.25Ta0.25Sc0.25)B2 has high enthalpy driving force, which more easily allows the formation of single-phase AlB2-type structures between components. The experiments further demonstrate that (Hf0.25Zr0.25Ta0.25Sc0.25)B2 possesses excellent phase stability, lattice integrity and nanoscale chemical homogeneity. (Hf0.25Zr0.25Ta0.25Sc0.25)B2 showed relatively high hardness (30.7 GPa), elastic modulus (E, G, and B of 522, 231 and 233 GPa, respectively), bending strength (454 MPa), and low thermal conductivity (13.9 W·m?1·K?1). The thermal expansion of (Hf0.25Zr0.25Ta0.25Sc0.25)B2 is higher than that of ZrB2 and HfB2 due to weakened bonding (M d - B p and M dd bonding) and enhanced anharmonic effects. Thus, incorporating Sc into high-entropy diborides can tailor the properties associated with the bonding, which further expands the compositional space of high-entropy diborides.  相似文献   

8.
《Ceramics International》2022,48(18):26400-26407
The high-entropy rare earth zirconate (La1/5Nd1/5Sm1/5Gd1/5Yb1/5)2Zr2O7 porous ceramics ((5RE1/5)2Zr2O7 PCs) were prepared using a foam-gel casting-freeze drying method combined with segmented calcination process. The results of SEM, TEM, and XRD analyses of the (5RE1/5)2Zr2O7 PCs indicated the formation of a defective fluorite crystal structure, with the rare earth elements homogeneously distributed. Meanwhile, the as-prepared (5RE1/5)2Zr2O7 PCs exhibited high porosity, low bulk density, low thermal conductivity, and relatively high compressive strength. Moreover, the high-temperature thermal conductivity of the samples was evaluated, and the results showed that the (5RE1/5)2Zr2O7 PCs maintain a thermal conductivity of 0.150 ± 0.002 W m?1 K?1 even at 1000 °C. The strategy used in this paper can be extended to the synthesis of other high-entropy porous ceramics with high porosity and low thermal conductivity, which is suitable for applications as thermal insulation materials.  相似文献   

9.
《Ceramics International》2020,46(3):3236-3241
Chemical doping is an indispensable tool to tailor the properties of the commercial piezoelectric materials. However, a high piezoelectric coefficient with enhanced thermal stability is rarely achieved by one dopant in some high-performance ferroelectrics, e.g., the recently discovered eco-friendly (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics. In order to optimize the piezoelectric property in BCZT system by a simple way, we investigated the doping effect of Fe3+, Nb5+ and Bi3+ cations in BCZT ceramics respectively. The results indicate that only Nb5+-doped BCZT ceramics display a combination of large piezoelectric coefficient and enhanced thermal stability, compared with others. Moreover, the established phase diagrams and in-situ transmission electron microscope (TEM) observations reveal that such optimized piezoelectric properties after Nb5+ doping originates from (i) the low polarization anisotropy near the ambient tetragonal (T)-orthorhombic (O) phase transition and (ii) the easy domain wall motion of persistent miniaturized ferroelectric domains upon heating.  相似文献   

10.
《Ceramics International》2020,46(17):26626-26631
A new high-entropy monoboride (Mo0.2Ta0.2Ni0.2Cr0.2W0.2)B ceramic with a WB-type orthogonal structure was designed and synthesised by in-situ reactive hot pressing at 2000 °C and 30 MPa for 1.5 h under an argon atmosphere. The microstructure of the sintered samples was comprehensively characterised, and the formation of a high-entropy monoboride (Mo0.2Ta0.2Ni0.2Cr0.2W0.2)B ceramic was confirmed. Owing to the high density of the dislocations and strengthening metal-boron bonds, the high-entropy (Mo0.2Ta0.2Ni0.2Cr0.2W0.2)B ceramic exhibited a hardness of 48.51 ± 4.07 GPa, which enabled it to be classed as a new superhard material. In addition, the thermal conductivity (2.05 ± 0.10 W/(m·K) at 400 °C) and electric conductivity (132.30 S/cm) were determined.  相似文献   

11.
《Ceramics International》2022,48(24):36084-36090
The high-entropy ceramic materials (Zr0.25Ce0.25Hf0.25Y0.25)O1.875 (H-0) and (Zr0.2Ce0.2Hf0.2Y0.2RE0.2)O1.8 (H-RE) (RE = La, Nd and Sm) with fluorite structure and homogeneous element distribution were prepared. With fluorite structure, fine grain size and high density, the H-0 and H-RE ceramics displayed low thermal conductivity, suitable thermal expansion coefficient, high hardness and fracture toughness. The effect of La, Nd and Sm on the mechanical, heat conductivity and heat expansion properties of high entropy ceramics were discussed. The single-phase high-entropy ceramic materials in this work are very suitable for application as thermal barrier materials.  相似文献   

12.
The high temperature microwave absorbing efficiency (HTMAE) of xLa0.9Sr0.1MnO3/(1 − x)MgAl2O4 composite ceramics was investigated by studying the crystal structure, electrical conductivity, and permittivity. The crystal structure of La0.9Sr0.1MnO3 and MgAl2O4 were maintained, but the Mn3+ and Al3+ ions were exchanged with each other through doping. The conductivity and permittivity of the composite ceramics increased with the increase of La0.9Sr0.1MnO3 content and test temperature. When x = 0.36, the electrical conductivity in La0.9Sr0.1MnO3 significantly enhanced the microwave polarization of the composite ceramics at high temperature. According to transmission/reflection modelling, the composite ceramics with x = 0.24 showed excellent HTMAE near the optimal thickness of 1.8 mm. Although the optimal thickness of the composite with x = 0.36 was reduced to 1.1 mm, the HTMAE was seriously lessened due to an impedance mismatch. xLa0.9Sr0.1MnO3/(1 − x)MgAl2O4 are promising as thin and efficient microwave absorbing materials at high temperatures and the microwave permittivity can be further enhanced by adjusting the conductivity of La0.9Sr0.1MnO3.  相似文献   

13.
Anti-spinel oxide SrY2O4 has attracted extensive attention as a promising host lattice due to its outstanding high-temperature structural stability and large thermal expansion coefficient (TEC). However, the overhigh thermal conductivity limits its application in the field of thermal barrier coatings. To address this issue, a novel high-entropy Sr(Y0.2Sm0.2Gd0.2Dy0.2Yb0.2)2O4 ceramic was designed and synthesized for the first time via the solid-state method. It is found that the thermal conductivity of Sr(Y0.2Sm0.2Gd0.2Dy0.2Yb0.2)2O4 is reduced to 1.61 W·m−1·K−1, 53 % lower than that of SrY2O4 (3.44 W·m−1·K−1) at 1500 °C. Furthermore, reasonable TEC (11.53 ×10−6 K−1, 25 °C ∼ 1500 °C), excellent phase stability, and improved fracture toughness (1.92 ± 0.04 MPa·m1/2) remained for the high-entropy Sr(Y0.2Sm0.2Gd0.2Dy0.2Yb0.2)2O4 ceramic, making it a promising material for next-generation thermal barrier coatings.  相似文献   

14.
A novel high‐entropy carbide ceramic, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C, with a single‐phase rock salt structure, was synthesized by spark plasma sintering. X‐ray diffraction confirmed the formation of a single‐phase rock salt structure at 26‐1140°C in Argon atmosphere, in which the 5 metal elements may share a cation position while the C element occupies the anion position. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C exhibits a much lower thermal diffusivity and conductivity than the binary carbides HfC, ZrC, TaC, and TiC, which may result from the significant phonon scattering at its distorted anion sublattice. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C inherits the high elastic modulus and hardness of the binary carbide ceramics.  相似文献   

15.
High-temperature thermal barrier coating (TBC) materials are desired for the development of high-efficient gas turbines and diesel engines. Herein, to meet up with this requirement, a new class of high-entropy fluorite-type oxides (HEFOs) has been synthesized via a solid-state reaction method. Comparing to La2Ce2O7, a promising TBC material, the HEFOs exhibit similar high thermal expansion coefficients (TECs) of 11.92×10−6∼12.11×10−6 K-1 at temperatures above 673 K but a better TEC matching performance at the temperature range of 473–673 K. It is also found that through tuning the average A-site cation radius, the TEC of the HEFOs could be tailored efficiently. The HEFOs also possess low thermal conductivities of 1.52-1.55 W∙m-1∙K-1 at room temperature, which is much lower than that of La2Ce2O7 and comparable to pyrochlores as Gd2Zr2O7. Moreover, the HEFOs display good sintering resistance and phase stability even at temperatures as high as 1873 K. The combination of these fascinating properties makes the HEFOs good candidates for thermal barrier coating and thermal insulating materials.  相似文献   

16.
High-entropy ceramics exhibit great application potential as thermal barrier coating (TBC) materials. Herein, a series of novel high-entropy ceramics with RE2(Ce0.2Zr0.2Hf0.2Sn0.2Ti0.2)2O7 (RE2HE2O7, RE = Y, Ho, Er, or Yb) compositions were fabricated via a solid-state reaction. X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) mapping analyses confirmed that RE2HE2O7 formed a single defect fluorite structure with uniform elemental distribution. The thermophysical properties of the RE2HE2O7 ceramics were investigated systematically. The results show that RE2HE2O7 ceramics have excellent high-temperature phase stability, high thermal expansion coefficients (10.3–11.7 × 10?6 K-1, 1200 ℃), and low thermal conductivities (1.10-1.37 W m-1 K-1, 25 ℃). In addition, RE2HE2O7 ceramics have a high Vickers hardness (13.7–15.0 GPa) and relatively low fracture toughness (1.14-1.27 MPa m0.5). The outstanding properties of the RE2HE2O7 ceramics indicate that they could be candidates for the next generation of TBC materials.  相似文献   

17.
《Ceramics International》2023,49(18):29729-29735
Herein, five new La2Zr2O7 based high-entropy ceramic materials, such as (La0.2Ce0.2Gd0.2Y0.2Er0.2)2Zr2O7, (La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7, (La0.2Gd0.2Y0.2Er0.2Sm0.2)2Zr2O7, (La0.2Ce0.2Y0.2Er0.2Sm0.2)2Zr2O7, (La0.2Ce0.2Gd0.2Y0.2Sm0.2)2Zr2O7), were synthesized using a sol-gel and high-temperature sintering (1000 °C) method. The spark plasma sintered (SPS) (La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7 pellet shows a low thermal conductivity of 1.33 W m-1 K-1 at 773 K, and it also exhibits better CaO–MgO–Al2O3–SiO2 corrosion resistance than that of Y2O3 stabilized ZrO2. It shows that (La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7 has a promising application potential as a thermal barrier coating.  相似文献   

18.
We report a large piezoelectric constant (d33), 720 pC/N and converse piezoelectric constant (d33*), 2215 pm/V for 0.55(Ba0.9Ca0.1)TiO3-0.45Ba(Sn0.2Ti0.8)O3 ceramics; the biggest value achieved for lead-free piezoceramics so far. The ceramic powders were calcined between 1050°C-1350°C and sintered at 1480°C. The best properties were obtained at a calcination temperature (CT) of 1350°C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 µm, ceramics density ~95%, and grain size ~40 µm led to a formation of orthorhombic-tetragonal-pseudo-cubic (O-T-PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (εr) >5000 and a low loss tangent (tan δ) of 0.029. In addition, the d33 value stabilizes in the range of 400-500 pC/N for all samples calcined between 1050°C and 1250°C. The results entail that the (Ba,Ca)(Sn,Ti)O3 ceramics are strong contenders to be a substitute for lead-based materials for room temperature applications.  相似文献   

19.
High-entropy perovskite thin films, as the prototypical representative of the high-entropy oxides with novel electrical and magnetic features, have recently attracted great attention. Here, we reported the electronic structure and charge transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films annealed at various temperatures. By means of X-ray photoelectron spectroscopy and absorption spectrum, it is found that the conduction-band-minimum shifts downward and the valence-band-maximum shifts upward with the increase of annealing temperature, leading to the narrowed band gap. Electrical resistance measurements confirmed a semiconductor-like behavior for all the thin films. Two charge transport mechanisms, i.e., the thermally-activated transport mechanism at high temperatures and the activation-less transport mechanism at low temperatures, are identified by a self-consistent analysis method. These findings provide a critical insight into the electronic band structure and charge transport behavior of Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, validating it as a compelling high-entropy oxide material for future electronic/energy-related technologies.  相似文献   

20.
Relaxor ferroelectrics are attracting an increasing interest in the application of pulse power systems due to their excellent energy storage performance. In this paper, the (1-x)(Ba0·85Ca0.15)(Zr0·1Ti0.9)O3-xBi(Mg0·5Ti0.5)O3 ((1-x)BCZT-xBMT, x ≤ 0.2) relaxor ceramics are prepared by the solid state method. The influence of BMT on the microstructure, dielectric and energy storage properties of the prepared ceramics is investigated. The XRD results show that the peak intensity of impurities (Bi2O3, TiO2 and Ba2Bi4Ti5O18) is gradually stronger than that of BCZT phase with x increasing. Meanwhile, the grain size of (1-x)BCZT-xBMT ceramics gradually increases on account of the appearance of impurities Bi2O3. Influenced by the impurities and BMT, the dielectric constant of prepared ceramics gradually decreases with x increasing. A large Wrec value of 0.65 J/cm3 with an ultrahigh η value of 97.89% is achieved at x = 0.15 due to the high breakdown strength and slim P-E hysteresis loop. Meanwhile, the η is insensitive to the electric field. The ultrahigh η leads to lesser energy loss during the charge and discharge process. It makes the 0.85BCZT-0.15BMT ceramic more attractive in the application of pulse power systems.  相似文献   

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