Collection of High-entropy Ceramics(202312)

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Enhanced Compatibility and Activity of High-entropy Double Perovskite Cathode Material for IT-SOFC
GUO Tianmin, DONG Jiangbo, CHEN Zhengpeng, RAO Mumin, LI Mingfei, LI Tian, LING Yihan
Journal of Inorganic Materials    2023, 38 (6): 693-700.   DOI: 10.15541/jim20220551
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Intermediate-temperature solid oxide fuel cell (IT-SOFC) is promising for carbon neutrality, but its cathode is limited by the contradiction between thermal compatibility and catalytic activity. Herein, we propose a high-entropy double perovskite cathode material, GdBa(Fe0.2Mn0.2Co0.2Ni0.2Cu0.2)2O5+δ (HE-GBO) with improved compatibility and activity, in view of the high-entropy strategy by multi-elemental coupling, which possesses double perovskite structure and excellent chemical compatibility with state-of-the-art Gd0.1Ce0.9O2-δ (GDC). The polarization resistance (Rp) of the symmetrical cells with HE-GBO cathode is 1.68 Ω·cm2 at 800 ℃, and the corresponding Rp of HE-GBO-GDC (mass ratio 7:3) composite cathode can be greatly reduced (0.23 Ω·cm2 at 800 ℃) by introducing GDC. Dendritic microchannels anode-supported single cells with HE-GBO and HE-GBO-GDC cathodes realize maximum power densities of 972.12 and 1057.06 mW/cm2 at 800 ℃, respectively, indicating that cell performance can be enhanced by high-entropy cathodes. The results demonstrate that high-entropy double perovskite cathode material HE-GBO has a high potantial to solve the conflict problem of thermal compatibility and catalytic activity in IT-SOFCs.

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High Entropy Oxide Ceramics (MgCoNiCuZn)O: Flash Sintering Synthesis and Properties
LI Wangguo, LIU Dianguang, WANG Kewei, MA Baisheng, LIU Jinling
Journal of Inorganic Materials    2022, 37 (12): 1289-1294.   DOI: 10.15541/jim20220320
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Flash sintering is a sintering technology coupled with temperature field and electric field, with characteristics of rapid mass transfer at low temperature, showing significant advantages in the synthesis of high entropy ceramics. In this study, relatively dense high entropy oxide ceramic (MgCoNiCuZn)O was synthesized by flash sintering, which properties were compared with those of conventional sintered samples. Under flash sintering condition of room temperature, the electric field intensity of 50 V/cm and the current density of 300 mA/mm2, the time of phase transformation is only 10 s. The maximum relative density of flash sintered sample is 94%, which is 22.8% higher than that of conventional sintered sample. The maximum hardness of flash sintered sample is 5.05 GPa, which is 3.95 GPa higher than that of conventional sintered sample. When the frequency is lower than 2 Hz, the dielectric constant of flash sintering sample is one order of magnitude higher than that of conventional sintered sample. The property improvement of flash sintered samples is attributed to the acceleration of mass transfer by the critical electric field to increase the material density, and the extra defects introduced by the critical electric field.

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Research Progress on the Flash Sintering Mechanism of Oxide Ceramics and Its Application
LIU Jinling, LIU Dianguang, REN Ke, WANG Yiguang
Journal of Inorganic Materials    2022, 37 (5): 473-480.   DOI: 10.15541/jim20210513
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Flash sintering is an electric field assisted sintering technology which has attracted much attention in recent years. This review introduces its origin, development, and basic characteristics. In the study of flash incubation and initiation process, the nonlinear conductivity characteristics and electrochemical blackening phenomenon are narrated, and the defect mechanism dominated by oxygen vacancy is recounted. As for rapid densification during flash sintering, it is proposed that the generation and movement of defects caused by electric field produce Coulomb force between powder particles, which is conducive to density in the early stage of flash sintering. Meanwhile, the densification process is accompanied by the rapid movement of metal cations. In terms of grain growth and microstructure evolution during the flash sintering, the sample temperature is asymmetrically distributed along the current direction, and the internal grain boundary mobility in the sample is significantly improved. During this stage, electrochemical defects exert a significant impact on the microstructure. Based on the above researches, we developed ceramic flash joining technology by using phenomenon of low-temperature rapid mass transfer under electric field, and realized rapid joining between similar kind of ceramics/ceramics, ceramics/metals, and even dissimilar ceramics/ceramics. A new ultrafast ceramic synthesis technology by flash sintering was developed, which not only realized the rapid synthesis of typical oxide ceramics, but also realized the rapid synthesis of high entropy ceramics and oxide ceramics with eutectic morphology. An electroplastic forming technology of oxide ceramics was developed, and a rapid tensile and bending deformation of zirconia ceramics at low temperature and low stress was preliminarily realized. Finally, this review summarizes the challenges in the field of flash sintering mechanism, and looks forward to the development direction of flash sintering from two aspects of Joule heating effect and nonthermal effect, aiming to be beneficial to the development of flash sintering technology in China.

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Inhibition of Lattice Thermal Conductivity of ZrNiSn-based Half-Heusler Thermoelectric Materials by Entropy Adjustment
WANG Pengjiang, KANG Huijun, YANG Xiong, LIU Ying, CHENG Cheng, WANG Tongmin
Journal of Inorganic Materials    2022, 37 (7): 717-723.   DOI: 10.15541/jim20210610
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The thermoelectric properties of ZrNiSn-based half-Heusler materials were hindered due to their high thermal conductivity. In order to reduce the lattice thermal conductivity, the high-entropy alloys ZrNiSn and Zr0.5Hf0.5Ni1-xPtxSn (x=0, 0.1, 0.15, 0.2, 0.25, 0.3) were prepared by levitation melting and spark plasma sintering. Configurational entropy of the alloys was manipulated by Hf substitution for Zr and Pt substitution for Ni. Effects of configuration entropy on the thermoelectric properties were investigated. The reslults showed that the minimum sum of lattice thermal conductivity and bipolar thermal conductivity (κl+κb) at 673 K for Zr0.5Hf0.5Ni0.85Pt0.15Sn was optimized at 2.1 W·m-1·K-1, which was significantly reduced by about 58% when compared with ZrNiSn. This finding provides an effective strategy for reducing lattice thermal conductivity of ZrNiSn-based alloy to offer great potential for further improvement of thermoelectrics.

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