Thermophysical and electrical properties of rare‐earth‐cerate high‐entropy ceramics

Abstract

A new series of rare‐earth‐cerate high‐entropy ceramics with compositions of (La0.2Nd0.2Sm0.2Gd0.2Dy0.2)2Ce2O7 (HEC1), (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Ce2O7 (HEC2), (La0.2Nd0.2Sm0.2Yb0.2Dy0.2)2Ce2O7 (HEC3), (La0.2Nd0.2Yb0.2Gd0.2Dy0.2)2Ce2O7 (HEC4), (La0.2Yb0.2Sm0.2Gd0.2Dy0.2)2Ce2O7 (HEC5) as well as a single component of Nd2Ce2O7 are fabricated via sintering the corresponding sol–gel‐derived powders at 1600°C for 10 h. HEC1–5 samples exhibit a single‐cerate phase with fluorite structure and high configurational entropy. Compared with Nd2Ce2O7, HEC1–5 samples have a lower grain growth rate owing to the sluggish diffusion effect. The chemical compositional uniformity of HEC1–5 as well as Nd2Ce2O7 does not apparently change after annealing at 1500°C for different time intervals (1, 6, 12, and 18 h). Compared with 8YSZ, HEC1–5 samples display the decreased thermal conductivity and increased thermal expansion coefficient. The lattice size disorder parameter of HEC1–5 is negatively related to the thermal conductivity in 26–450°C. Furthermore, HEC1–5 and Nd2Ce2O7 exhibit lower oxygen‐ion conductivity, meaning an increased resistance to oxygen diffusion.

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

“…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 .…”

“…Owing to co‐doping of multiple RE ions, some RE ions may indeed undergo valence bond leaps during the substitution process to produce oxygen vacancies and the density of the oxygen vacancies are uncertain, so there is no significant linear relationship among g , δ , Δ d , and σ . Furthermore, the large differences between the concentrations and masses of the multiple principal RE ions, the interaction between different ions, and lattice distortion, which causes ion diffusion hysteresis 55 . That is, under the effect of HE hysteresis diffusion, the diffusion of oxygen ions becomes slower; thus, the σ values of 5–8HERN are lower than those of RENbO 4 ceramics.…”

“…Furthermore, the large differences between the concentrations and masses of the multiple principal RE ions, the interaction between different ions, and lattice distortion, which causes ion diffusion hysteresis. 55 That is, under the effect of HE hysteresis diffusion, the diffusion of oxygen ions becomes slower; thus, the σ values of 5-8HERN are lower than those of RENbO 4 ceramics. In addition, the grain size affects the conductivity of ceramics, where a smaller grain size can reduce the oxygen-ion conductivity.…”

High-entropy rare earth materials: synthesis, application and outlook

“…Notably, the fracture toughness of the dualphase composite ceramics initially increased to a maximum, and then sharply decreased as the mole fraction of HA increased from 0 to 50%. Moreover, a novel set of HE-RE cerate ceramics was successfully synthesized using Nd 2 Ce 2 O 7 as the basic component through sintering sol-gel-derived powders at 1600 1C for 10 h. 161 All the HE-RE cerate samples exhibited a single-phase cerate structure with a fluorite arrangement, characterized by high configurational entropy. Compared to Nd 2 Ce 2 O 7 , they displayed a lower rate of grain growth due to the sluggish diffusion effects.…”

Dielectric and energy storage properties of (Ba0.2Sr0.2Na0.2Ca0.2La0.2)(ZrxTi1‐x)O3 high‐entropy ceramics and thin films

“…Originating from high-entropy alloys (HEAs), HECs typically consist of a single-phase solid solution formed by five or more equimolar ions occupying the cation/anion sub-sites of the ceramic lattice. [18][19][20][21][22] The "cocktail effect" produced by mixing different ions in the same site of lattice in HECs can improve their intrinsic characteristics and achieve unique properties. Because of the huge lattice distortion and elemental sluggish diffusion, the growth of grains is inhibited and the microstructure with fine grains is obtained.…”