A high-entropy (Bi0.2Na0.2K0.2Ba0.2Ca0.2)TiO3 (BNKBCT) ceramic is successfully fabricated by using flash sintering technique. The synthesis and densification of BNKBCT are simultaneously carried out ...by a stepwise current-ramping flash sintering process. Despite the presence of excessive Na+ and K+ ions, single-phase perovskite ceramics are obtained with uniform elemental distribution. The dielectric characterization reveals the relaxor ferroelectric nature of BNKBCT ceramic. Moreover, the discharge energy storage density and efficiency of the as-prepared BNKBCT ceramic are 0.684 J/cm3 and 87.5% under the electric field of 129 kV/cm, respectively. These results indicate that the introduction of high entropy is a viable strategy to tune the properties of electrical ceramics.
The composition and synthesis approach of high entropy ceramics have significant influences on their microstructures and mechanical properties. A new (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2 high entropy ...diboride ceramic with excellent mechanical properties was successfully prepared by spark plasma sintering (SPS) at a relatively “low temperature” (1800 °C) in this work. The effects of two mixing strategies, grinding and ball milling, on the solid solubility of the calcined powders were studied. Furthermore, the effects of these two mixing strategies on the phase and morphology of the calcined powders and the mechanical properties of the SPS sintered ceramics were analyzed. Experimental results indicated that, compared with a single solid solution phase within the high entropy boride powders obtained by ball milling, incomplete solid-solution presented in the high entropy boride powders obtained using grinding treatment. It promoted the solid-state diffusion and in-situ reaction of the diborides in the ceramics during the sintering process, thereby improving the densification and the hardness of the high entropy diboride ceramics. By grinding treatment, (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2 high entropy ceramic with a relative density of 94% and a hardness of up to 25.34 ± 1.5 GPa at an indentation load of 9.8 N was obtained at 1800 °C. This work not only expanded the family of high-entropy diboride ceramics but also proved the advantage of grinding treatment in preparation of high entropy diboride ceramics.
•GLNSYMnO3 has a single-phase orthorhombic perovskite structure sintered at 1250 °C.•The high configurational entropy drives the structural stability of GLNSYMnO3 even at temperatures below ...TC.•GLNSYMnO3 has good magnetism due to the lattice distortion and double-exchange.•GLNSYMnO3 is a second-order magnetic phase transition material with potential applications in magnetic storage.
Rare-earth transition element high-entropy perovskite ceramics (HEPCs) (Gd0.2La0.2Nd0.2Sm0.2Y0.2)MnO3 (GLNSYMnO3) were prepared by using a solid-state reaction method, and the structure, morphology and magnetic properties of the GLNSYMnO3 were studied. The crystalline structure of GLNSYMnO3 is a smooth surface and similar to “cashews” tubular particles, and a single-phase orthorhombic (Pbnm Space group) perovskite without impurities is confirmed when the sintered temperature reaches or exceeds 1250 °C by the analysis of phase composition and microstructures. Magnetic measurements indicate that GLNSYMnO3 HEPCs have low Curie temperature (TC = 61 K), but they exhibit a good magnetism by comparison with other high-entropy ceramics, which is caused by the lattice distortion and exchange interactions between high concentrations of Mn3+ (92.4 %) and non-magnetic oxygen ions, promoting the movement of circulating electrons. GLNSYMnO3 HEPCs did not undergo a phase transition below TC due to high configurational entropy driving structural stability. In addition, GLNSYMnO3 HEPCs undergo a second-order magnetic phase transition from isothermal magnetization curves and Arrot curves, which have potential applications in magnetic storage.
A new entropy-stabilized rare earth niobates (RE3NbO7, RE = Dy, Y, Ho, Er, Yb) system with disordered defective fluorite structure was prepared by solid-state method. XRD, Raman and EDS results ...confirmed the homogeneous distribution and equimolar doping of rare earth cations. High-entropy RE3NbO7 ceramics showed smaller grain size compared with single rare earth niobates owing to the sluggish grain diffusion. Due to the increased configuration entropy, (Dy0.2Ho0.2Er0.2Y0.2Yb0.2)3NbO7 (5RE3NbO7) has enhanced mechanical properties (Hv = 9.51 GPa, KⅠC = 2.13 MPa m0.5), a high thermal expansion coefficient (10.2 × 10−6 K-1, 1200℃) and ultra-low thermal conductivity (0.724 W m-1 K-1, 25℃). These results suggest that the material can be used as a new type of thermal barrier coatings as alternative to yttria-stabilized zirconia.
•High-entropy rare-earth zirconate ceramics demonstrated extreme resistance to CMAS corrosion.•There are no horizontal and vertical cracks in the ceramic substrate and the reaction layer of the HEZ ...sample respectively.•The HEZ suffered from CMAS corrosion only through dissolution and re-precipitation, while additional grain boundary corrosion existed in the LZ.
The corrosion resistance to calcium-magnesium-alumino-silicates (CMAS) is critically important for the thermal barrier coatings (TBCs). High-entropy zirconate (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEZ) ceramics with low thermal conductivity, high coefficient of thermal expansion and good durability to thermal shock is expected to be a good candidate for the next-generation TBCs. In this work, the CMAS corrosion of HEZ at 1300°C was firstly investigated and compared with the well-studied La2Zr2O7 (LZ). It is found that the HEZ ceramics showed a graceful behavior to CMAS corrosion, obviously much better than the LZ ceramics. The HEZ suffered from CMAS corrosion only through dissolution and re-precipitation, while additional grain boundary corrosion existed in the LZ system. The precipitated high-entropy apatite showed fine-grained structure, resulting in a reaction layer without cracks. This study reveals that HEZ is a promising candidate for TBCs with extreme resistance to CMAS corrosion.
A new class of high-entropy perovskite oxides (i.e., multiple-cation solid solutions with high configurational entropies) has been synthesized. Six of the 13 compositions examined, including ...Sr(Zr0.2Sn0.2Ti0.2Hf0.2Mn0.2)O3, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Ce0.2)O3, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Y0.2)O3−x, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 and (Sr0.5Ba0.5)(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, can form homogeneous single solid-solution phases. Goldschmidt's tolerance factor, instead of cation-size difference, influences the formation and temperature-stability of single cubic perovskite solid solutions. This new class of multicomponent (high-entropy) perovskite solid solutions with distinct and highly-tunable chemistries can enable simultaneous tailoring of multiple properties and potentially lead to new functionality.
The formation of a homogenous solid solution of perovskite Sr(Zr0.2Sn0.2Ti0.2Hf0.2Mn0.2)O3, which is one example of the six high-entropy perovskite oxides synthesized in this study. Display omitted
•High-entropy BNKBT-SMN ceramics for dielectric energy storage were design and prepared.•A high Wrec of 3.37 J/cm3and high η of 80 % at low electric fields were achieved.•The excellent stability in ...energy storage has been achieved in 0.88BNKBT-0.12SMN.
High-entropy perovskite oxides in (Bi0.4Na0.2K0.2Ba0.2)TiO3- Sr(Mg1/3Nb2/3)O3 system were designed and prepared for dielectric energy storage. The effects of composition and sintering temperature on energy storage performance were investigated. The temperature-and frequency-dependent energy storage performance was characterized. A ceramic with a recoverable energy storage density of 3.37 J/cm3 and an energy storage efficiency of 80 % was obtained at 310 kV/cm. The energy density is one of the best ever reported at low electric fields. The current result provides an idea for developing high-entropy dielectric energy storage ceramics.
•18 compositionally-complex (medium- and high-entropy) pyrochlore oxides fabricated.•Mixing of cations at A- and/or B-sites leads to reduced thermal conductivity.•Thermal conductivity correlates well ...with a modified size disorder parameter.•A new descriptor proposed for designing low-k medium- and high-entropy ceramics.•Medium-entropy ceramics can outperform their high-entropy counterparts.
High-entropy ceramics generally exhibit reduced thermal conductivity, but little is known about what controls this suppression and which descriptor can predict it. Herein, 22 single-phase pyrochlores were examined. Up to 35% reductions in thermal conductivity were achieved in medium- and high-entropy compositions with retained moduli, thereby attaining insulative yet stiff properties for thermal barrier coating applications. Notably, the measured thermal conductivity correlates well with a modified size disorder parameter δSize*, thereby suggesting the importance of severe lattice distortion. Thus, this δSize* is suggested as a useful descriptor for designing thermally-insulative compositionally-complex ceramics, where medium-entropy ceramics can outperform their high-entropy counterparts.
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A series of rare earth zirconates (RE2Zr2O7) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La2Zr2O7 and Yb2Zr2O7, the smaller “rattling” ions (Yb3+, Er3+, ...Y3+) have been incorporated into pyrochlore lattice in (La0.2Nd0.2Y0.2Er0.2Yb0.2)2Zr2O7 (LNYEY) while larger ions (La3+, Nd3+, Sm3+, Eu3+) incorporated into fluorite lattice in (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb3+, Er3+, and Y3+, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m-1 K-1, 100-600℃) than LNSGY (1.74-1.75 W m-1 K-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, Hv = 11.47 ± 0.41 GPa; LNSGY, Hv = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10-6 K-1, 1000℃; LNSGY, 11.02 × 10-6 K-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings.
The chemical homogeneity of single phase high‐entropy AlB2‐type Ti‐Zr‐Hf‐Ta‐TM diboride (TM = Cr, V, W, Mo), as well as Ti‐Zr‐Hf‐Mo‐W solid solutions was investigated using a new method based on the ...comparative examination of information provided by electron microscopy and structural parameters. The study of the densification behavior was accomplished, and strong correlations among densification rate‐grain coarsening‐long range chemical randomization were found. High‐resolution synchrotron radiation X‐ray diffraction supported by grain‐scale chemical analyses by energy dispersive spectroscopy indicated that homogenization of the metals was incomplete, with direct impact on the refined lattice μ‐strain. The chemical inhomogeneity was on the same length scale as the grain size, which makes it hardly detectable by typical chemical mapping using energy dispersive spectroscopy. Based on this analysis, the resulting μ‐strain broadening is not an intrinsic property of the material, but strongly depends on its processing history.
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