Study on the Solid Solution Structures of High-Entropy Ceramics by Transmission Electron Microscopy

Abstract: High-entropy brings high-entropy effect on thermodynamics, lattice distortion effect on structure, diffusion retardation effect on dynamics and “cocktail” effect on properties in materials. It is a hotspot to improve the properties of ceramics by high-entropy design. However, it still lacks the study of high-entropy structures and their correlation to the properties through transmission electron microscopy (TEM). In this study, high-entropy borides and carbides powders were fabricated by using metal oxides, boron carbide and graphite as raw materials. The high-entropy (TiZrHfNbTa)B2 and (TiZrHfNbTa)C ceramics were then synthesized by spark plasma sintering of the as-fabricated powders. Transmission electron microscope and energy dispersive spectrometry were used to characterize the structure of the two high-entropy ceramics at the nano-scale and atomic-scale. The integrity of crystal structure was maintained after solid solution of five transition metal elements which were found to be uniformly distributed in the ceramics. However, at atomic scales, concentration oscillations of solid solution elements, atomic dispersion and lattice strain were observed. The solid solution structures at atomic scales as-obtained in this work will help to understand the structure-property relationship of high-entropy ceramics and provide experimental basis for the composition and structure design of high-entropy ceramics.

Key words: high-entropy ceramics; TEM; structure in nano-scale; structure in atomic-scale

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