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It is generally reported that the grain growth in high-entropy ceramics at high temperatures is relatively slower than that in the corresponding single-component ceramics owing to the so-called sluggish diffusion effect. In this study, we report a fast grain growth phenomenon in the high-entropy ceramics (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)MgAl11O19 (HEMA) prepared by a conventional solid-state reaction method. The results demonstrate that the grain sizes of the as-sintered HEMA ceramics are larger than those of the corresponding five single-component ceramics prepared by the same pressureless sintering process, and the grain growth rate of HEMA ceramics is obviously higher than those of the five single-component ceramics during the subsequent heat treatment. Such fast grain growth phenomenon indicates that the sluggish diffusion effect cannot dominate the grain growth behavior of the current high-entropy ceramics. The X-ray photoelectron spectroscopy (XPS) analysis reveals that there are more oxygen vacancies (OV) in the high-entropy ceramics than those in the single-component ceramics owing to the variable valance states of Eu ion. The high-temperature electrical conductivities of the HEMA ceramics support this analysis. It is considered that the high concentration of OV and its high mobility in HEMA ceramics contribute to the accelerated migration and diffusion of cations and consequently increase the grain growth rate. Based on this study, it is believed that multiple intrinsic factors for the high-entropy ceramic system will simultaneously determine the grain growth behavior at high temperatures.


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Fast grain growth phenomenon in high-entropy ceramics: A case study in rare-earth hexaaluminates

Show Author's information Lin ZHOUJi-Xuan LIU( )Tian-Zhe TUYue WUGuo-Jun ZHANG( )
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Institute of Functional Materials, Donghua University, Shanghai 201620, China

Abstract

It is generally reported that the grain growth in high-entropy ceramics at high temperatures is relatively slower than that in the corresponding single-component ceramics owing to the so-called sluggish diffusion effect. In this study, we report a fast grain growth phenomenon in the high-entropy ceramics (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)MgAl11O19 (HEMA) prepared by a conventional solid-state reaction method. The results demonstrate that the grain sizes of the as-sintered HEMA ceramics are larger than those of the corresponding five single-component ceramics prepared by the same pressureless sintering process, and the grain growth rate of HEMA ceramics is obviously higher than those of the five single-component ceramics during the subsequent heat treatment. Such fast grain growth phenomenon indicates that the sluggish diffusion effect cannot dominate the grain growth behavior of the current high-entropy ceramics. The X-ray photoelectron spectroscopy (XPS) analysis reveals that there are more oxygen vacancies (OV) in the high-entropy ceramics than those in the single-component ceramics owing to the variable valance states of Eu ion. The high-temperature electrical conductivities of the HEMA ceramics support this analysis. It is considered that the high concentration of OV and its high mobility in HEMA ceramics contribute to the accelerated migration and diffusion of cations and consequently increase the grain growth rate. Based on this study, it is believed that multiple intrinsic factors for the high-entropy ceramic system will simultaneously determine the grain growth behavior at high temperatures.

Keywords: electrical conductivity, high-entropy ceramics, rare-earth hexaaluminate, fast grain growth

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Publication history

Received: 28 May 2022
Revised: 28 September 2022
Accepted: 30 September 2022
Published: 23 December 2022
Issue date: January 2023

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© The Author(s) 2022.

Acknowledgements

We acknowledge the financial support from the National Natural Science Foundation of China (Nos. 52032001 and 52211540004) and the Fundamental Research Funds for the Central Universities (No. 2232021A-01).

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