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 influenc...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(O_(vac))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(Ca_(x)Ce_(y1)Zr_(y2)Hf_(z)Sn_(z)Ti_(z))O_(2−δ)HEFOs.High mass/size disorder and an appropriate Ovac(10%)result in(Ca_(0.2)Ce_(0.1)4Zr_(0.1)2Hf_(0.18)Sn_(0.18)Ti_(0.18))O_(2−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,(La_(_(0.3))Y_(_(0.3))Ce_(0.2)Nb_(0.1)Ta_(0.1))O_(2−δ),and(Yb_(0.52)Ce_(0.12)Zr_(0.12)Sn_(0.12)Nb_(0.12))O_(2−δ).This design approach will provide a valuable reference for the design of other high-entropy oxides.展开更多
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.Comb...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℃ 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.展开更多
基金supported by the Fundamental Research Funds for the Central Universities(Nos.2023YJS062 and 2022JBZY025)the State Key Laboratory of New Ceramic and Fine Processing,Tsinghua University(No.KFZD201902)the Beijing Government Funds for the Constructive Project of Central Universities.
文摘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(O_(vac))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(Ca_(x)Ce_(y1)Zr_(y2)Hf_(z)Sn_(z)Ti_(z))O_(2−δ)HEFOs.High mass/size disorder and an appropriate Ovac(10%)result in(Ca_(0.2)Ce_(0.1)4Zr_(0.1)2Hf_(0.18)Sn_(0.18)Ti_(0.18))O_(2−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,(La_(_(0.3))Y_(_(0.3))Ce_(0.2)Nb_(0.1)Ta_(0.1))O_(2−δ),and(Yb_(0.52)Ce_(0.12)Zr_(0.12)Sn_(0.12)Nb_(0.12))O_(2−δ).This design approach will provide a valuable reference for the design of other high-entropy oxides.
基金supported by the Fundamental Research Funds for the Central Universities(Grant Nos.2020YJS148 and 2022JBZY025)State Key Laboratory of New Ceramics and Fine Processing Tsinghua University(Grant No.KFZD201902)+1 种基金Beijing Natural Science Foundation(Grant No.2182059)the Beijing Government Funds for the Constructive Project of Central Universities.
文摘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℃ 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.
