Entropy-Driven Structural Evolution in Ceramic Oxides.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• High-entropy ceramics (HECs) offer diverse properties due to multiple elements randomly occupying crystallographic sites.
• Limited exploration of HECs with dissimilar elements due to enthalpic barriers hindering entropic stabilization.
• Existing HECs often contain few, similar elements, restricting understanding of entropy's role.

Purpose of the Study:

• To model and experimentally realize complex high-entropy ceramics with a wide range of elements.
• To investigate the influence of increasing entropy on structural and configurational disorder in ceramics.
• To provide insights into entropy-driven stabilization of compositionally complex ceramic materials.

Main Methods:

• Density functional theory (DFT) modeling of fluorite crystal structures (1-10 elements).
• Experimental synthesis of fluorite oxide nanostructures with varying metal content (1, 3, 8, 15, and 25 elements).
• Characterization of structural and thermal properties as a function of elemental composition and entropy.

Main Results:

• Successful modeling and synthesis of HECs with up to 25 diverse elements, including rare-earth, transition, alkaline, p-block, and noble metals.
• Demonstrated correlation between increasing entropy and rising structural/configurational disorder.
• Observed alterations in lattice distortion, crystallinity, homogeneity, defect density, and thermal stability with increased entropy.

Conclusions:

• Entropy plays a crucial role in stabilizing compositionally complex ceramics.
• The developed 25-element HEC represents a record in compositional complexity.
• This work expands the understanding and potential applications of high-entropy materials.