Microstructure and electrical properties of new high-entropy rare-earth zirconates

Wang, Yuhao; Jin, Yongxing; Ding, Zhao-Ying; Cao, Guojian; Liu, Zhan‐Guo; Ouyang, Jun; Wang, Yujin

doi:10.1016/j.jallcom.2022.164331

“…In recent years, much attention has been paid to high-entropy RE-containing mixed oxides such as perovskites, , tantalites, tantalates, , niobates, , silicates, zirconates, − molybdates, and aluminates , due to their high potential as advanced ceramic materials possessing improved mechanical, thermal, and electrical properties . Cerium-based RE oxides with a fluorite structure have attracted researchers’ interest − since their semiconducting property can easily be tuned by chemical composition .…”

Section: Introductionmentioning

confidence: 99%

High-Entropy Layered Rare Earth Hydroxides

Теплоногова

¹

,

Yapryntsev

²

,

Baranchikov

³

et al. 2022

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New high-entropy layered rare earth hydroxides � (Y,Eu,Gd,Er,Sm) 2 (OH) 5 NO 3 , (Y,Eu,Gd,Er,Tb) 2 (OH) 5 NO 3 , (Y,Eu,Gd,Er,Yb) 2 (OH) 5 NO 3 , (Y,Eu,Gd,Er,Nd) 2 (OH) 5 NO 3 , and (Y,Eu,-Gd,Er,Nd,Sm,Tb) 2 (OH) 5 NO 3 � were obtained using a hydrothermal microwave method. The annealing of layered rare earth hydroxides at 900 °C resulted in the corresponding high-entropy rare earth oxides. Based on inductively coupled plasma atomic emission spectroscopy data, the values for configurational entropy for both rare earth hydroxides and oxides were estimated, confirming the formation of high-entropy compounds. Energy-dispersive X-ray spectroscopy mapping, including mapping in the scanning transmission microscopy mode, showed no signs of chemical segregation and confirmed uniform rare earth elements' distribution both in the particles of high-entropy layered basic nitrates and in the particles of high-entropy oxides. The ratios of rare earth cations in the initial aqueous solutions of mixed nitrates were close to the ratios of cations in the resulting high-entropy layered rare earth basic nitrates and high-entropy rare earth oxides.

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“…The oxygen‐ion conductivities of 5–8HERN are compared to those of other potential TBC materials at 750°C (Table 2), which are much lower than those of 8YSZ, 7 HE cerate (La 0.2 Yb 0.2 Sm 0.2 Gd 0.2 Dy 0.2 ) 2 Ce 2 O 7 (HECe), 55 HE zirconate (Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Dy 0.2 ) 2 Zr 2 O 7 (HEZr), 56 and an HE oxide (Hf 0.25 Zr 0.25 Ce 0.25 Y 0.25 )O 2− δ (HZCYO), 57 and close to that of an entropy‐stabilized oxide (Mg 0.2 Co 0.2 Ni 0.2 Zn 0.2 Cu 0.2 )O 2 (MCNZCO) 58 . A comparison of the Arrhenius curves of HE niobates with 8YSZ and other HE oxides (Figure 7C) shows that σ of 5–8HERN are much smaller than those of 8YSZ and other HE RE oxides, and slightly higher than those of HE fluorite oxides (Mg 0.2 Co 0.2 Ni 0.2 Zn 0.2 Cu 0.2 )O 2 .…”

Section: Resultsmentioning

confidence: 92%

“…The ionic conductivity gradually increases with increasing temperature, indicating that the migration of oxygen ions occurs during heating. The oxygen-ion conductivities of 5-8HERN are compared to those of other potential TBC materials at 750 • C (Table 2), which are much lower than those of 8YSZ, 7 56 and an HE oxide (Hf 0.25 Zr 0.25 Ce 0.25 Y 0.25 )O 2−δ (HZCYO), 57 and close to that of an entropy-stabilized TA B L E 2 Oxygen-ion conductivity of 5-8HERN compared to other potential thermal barrier coating (TBC) materials at 750 • C. 7D). A higher E a means that more energy is required for a chemical reaction to occur and the system is more stable.…”

Section: Oxygen-ion Conductivitymentioning

confidence: 99%

New class of high‐entropy rare‐earth niobates with high thermal expansion and oxygen insulation

Liu

¹

,

Gan

²

,

Wang

³

et al. 2023

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“…2) provide a complementary bond length information compared with the XRD results. The overall Raman-active modes are weak owing to disorder atom sites of high-entropy crystal lattice [29], whereas Ce0.25 and Ce0.5 present board Raman peaks due to disorder cations and anions in fluorite structure. The wave number T 2g (approximately 394 cm −1 ) of pyrochlore phase B-O1 stretching mode increases as the bond length of B-O decreases (Hf 4+ doping) [30].…”

Section: Resultsmentioning

confidence: 97%

Influence of order-disorder transition on the mechanical and thermophysical properties of A2B2O7 high-entropy ceramics

Zhu

¹

,

Wei²,

Xu³

et al. 2022

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The order-disorder transition (ODT) of A2B2O7 compounds obtained enormous attention owing to the potential application for thermal barrier coating (TBC) design. In this work, the influence of ODT on the mechanical and thermophysical properties of dual-phase A2B2O7 high-entropy ceramics was investigated by substituting Ce4+ and Hf4+ with different ionic radii on B-sites (Zr4+). The X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) results show that $$r_{\rm{A}^{3+}}/r_{\rm{B}^{4+}}=1.47$$ r A 3 + / r B 4 + = 1.47 is the critical value of ODT phase boundary with different doping B-site ion contents, and the energy dispersive spectroscopy (EDS) results further indicate the uniform distribution of elements. Interestingly, owing to the high intrinsic disorder derived from high-entropy effect, the A2B2O7 high-entropy ceramics exhibit unreduced modulus (E0 ≈ 230 GPa) and enhanced mechanical properties (HV ≈ 10 GPa, KIC ≈ 2.3 MPa·m0.5). A2B2O7 high-entropy ceramics exhibit excellent thermal stability with relatively high thermal expansion coefficients (TECs) (Hf0.25, 11.20×10−6 K−1, 1000 °C). Moreover, the matching calculation implied that the ODT further enhances the phonon scattering coefficient, leading to a relatively lower thermal conductivity of (La0.25Eu0.25Gd0.25Yb0.25)2(Zr0.85Ce0.15)2O7 (1.48–1.51 W/(m·K), 100–500 °C) compared with other components. This present work provides a novel composition design principle for high-entropy ceramics, as well as a material selection rule for high-temperature insulation applications.

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Microstructure and electrical properties of new high-entropy rare-earth zirconates

Cited by 21 publications

References 63 publications

High-Entropy Layered Rare Earth Hydroxides

High-Entropy Layered Rare Earth Hydroxides

New class of high‐entropy rare‐earth niobates with high thermal expansion and oxygen insulation

Influence of order-disorder transition on the mechanical and thermophysical properties of A2B2O7 high-entropy ceramics

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