Many factors impact the formability of single phase high-entropy pyrochlore ceramics (HEPCs) which become a research hotspot owing to their excellent properties. To investigate the effect of size disorder, two combinations with same mixing entropy and different size disorder were designed, thermodynamic analysis of first-principles calculations and experimental research were conducted in this paper. The calculation results reveal that the enthalpy change decreases significantly with the decrease of size disorder, promoting the synthesis of singlephase high-entropy pyrochlore. The experimental results prove that the combination with lower size disorder leads to single-phase HEPCs, and the prepared material exhibits low thermal conductivity (1.68 W/(m & sdot; K)) and low theoretical density (5.73 g/cm 3 ).

High-entropy fluorite oxides (HEFOs) show significant potential for thermal protection applications due to their advantageous combination of low thermal conductivity and high Yong’s modulus. However, the factors influencing its formation have not been well studied, and a systematic method for compositional design has not yet been established. In this paper, the effects of oxygen vacancy concentration (Ovac) and mean cation radius (r¯) on formability of HEFOs were investigated to develop a compositional design approach. The results indicate that an appropriate r¯ and Ovac is crucial for promoting the formability of single-phase (CaxCey1Zry2HfzSnzTiz)O2−δ HEFOs. High mass/size disorder and an appropriate Ovac (10%) result in (Ca0.2Ce0.14Zr0.12Hf0.18Sn0.18Ti0.18)O2−δ exhibiting the lowest thermal conductivity of 1.24 W·m−1·K−1. Building upon these insights and employing a valence combination strategy, three new single-phase HEFOs with low thermal conductivity were successfully designed and synthesized, namely, (La0.28Y0.28Ce0.18Zr0.18W0.08)O2−δ, (La0.3Y0.3Ce0.2Nb0.1Ta0.1)O2−δ, and (Yb0.52Ce0.12Zr0.12Sn0.12Nb0.12)O2−δ. This design approach will provide a valuable reference for the design of other high-entropy oxides.

In this paper, a series of (Ce0.2Zr0.2Ti0.2Sn0.2Y0.2-xCax)O2-delta (x = 0-0.2) high-entropy of compositionally-complex ceramics were prepared using solid-state reaction method. The results showed that the content of Ca2+ had significant effects on the phase composition, microstructure and properties of the prepared materials. As Ca2+ content increased, single-phase fluorite was easier to form. When x <= 0.05, materials contained dual-phase of fluorite and pyrochlore structures. When x >= 0.075, the prepared materials showed single-phase fluorite structure, which indicated that high-entropy fluorite ceramics (HEFCs) could be prepared under this condition. When Ca2+ content increased from 0.075 to 0.2, grain size of HEFCs decreased, and relative density decreased from 95.7 % to 78.6 %. Thermal conductivity of these HEFCs varied from 1.87 W m- 1 K-1 to 1.60 W m- 1 K-1, which was lower than 8YSZ. As Ca2+ content increased, both size disorder and mass disorder increased too leading to low thermal conductivity. The results indicate that the prepared HEFCs are promising for thermal insulation applications.

A set of medium-/high-entropy pyrochlore oxides (M-HEPOs) with different compositions were designed and synthesized. The phase compositions of the prepared materials were determined through X-ray diffraction and Raman spectroscopy. Among the 24 designed samples, two high-entropy and six medium-entropy samples formed single-phase pyrochlore materials, two medium-entropy samples formed dual-phase pyrochlore materials, and the others formed multiphase materials dominated by the pyrochlore phase. The factors affecting the formation of single-phase pyrochlore structure were studied. The results revealed that size disorder is a major element determining the formation of single-phase pyrochlore, whereas mixing entropy has minimal effect. It is anticipated that this study will provide significant insights into the effects of size disorder and mixing entropy on the formation of M-HEPOs.

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.

In this paper, we report the design and synthesis of La3+ based high-entropy pyrochlore ceramics (HEPCs) with five different B-site cations using the valence combination strategy. The factors affecting the formation of pyrochlore phase have been investigated. The result reveals that both valence disorder and size disorder can significantly affect the formability of pyrochlore phase, and the formability increases as the two disorders decrease. Following this guideline, a set of new HEPCs with single phase have been successfully synthesized.

In this paper, cordierite-based porous ceramics with magnetic properties have been firstly in-situ synthesized by using MgO, Al 2 O 3 , and SiO 2 powders as raw materials and Fe 3 O 4 as a functional additive. Combining with the foam freeze casting method, near net size fabrication (total linear shrinkage < 2.86%) of the magnetic porous materials was realized by adjusting the amount of Fe 3 O 4 . The porosity, compressive strength, and saturation magnetization of the prepared materials were 83.9%–87.8%, 1.51–2.65 MPa, and 1.2–5.8 emu/g, respectively. The phase composition and microstructure evolutions during sintering were investigated briefly. The results showed that the synthesis temperature of cordierite was lowered about 100 °C due to the addition of Fe 3 O 4 . Except for the main phase-cordierite, Mg—Al—Fe spinel and α-Fe 2 O 3 also existed in the final materials. The lattice parameters of the Mg—Al—Fe spinel and the amount of α-Fe 2 O 3 changed obviously with the change in the sintering temperature and Fe 3 O 4 amount, which mainly influenced the magnetic properties of the prepared materials. Thus, a facile fabrication method of the cordierite-based porous ceramics with the magnetic properties has been put forward in this paper.

Single-phase (Ce0.2Zr0.2Ti0.2Sn0.2Ca0.2)O2-delta porous high-entropy ceramics have been in-situ fabricated by foamgelcasting-freeze drying method at different temperatures. The microstructure, phase composition, and properties of the obtained ceramics were investigated. The results indicate that compared with other porous ceramics reported in the literatures, this type of ceramics exhibits excellent performance. The sample prepared at 1350 degrees C shows high porosity (88.6 %), low thermal conductivity (0.023 W m(-1) K-1), and high compressive strength (1.48 MPa). The current study suggests that porous (Ce0.2Zr0.2Ti0.2Sn0.2Ca0.2)O2-delta high entropy ceramics are promising candidates for thermal insulation applications.