Fabrication of Ceramic Material

1. Introduction

Ceramics are an essential class of materials used for thousands of years due to their unique properties. They are inorganic non-metallic materials widely used in applications such as construction (Maged et al., 2023), electronics (Cao et al., 2023), biomedical (Lakshmi Priya et al., 2017), and energy due to their excellent thermal (Smith & Naït-Ali, 2021), mechanical (Ke et al., 2023), and electrical properties (Guo et al., 2023). Traditional ceramics are typically made of a single or a few elements, such as alumina or zirconia, and exhibit a relatively ordered structure (Wright & Luo, 2020). In recent years, a new class of ceramics called high entropy ceramics (HECs) has emerged. HECs are characterized by a high degree of structural complexity and disorder due to the mixing of multiple elements in almost equal proportions (Gild et al., 2016). Mixing multiple elements in high entropy ceramics results in a significant entropy increase, leading to their distinctive properties, including elevated hardness (Qin et al., 2021), enhanced strength (Iwan et al., 2022), and robust thermal stability (Li et al., 2019), setting them apart from conventional ceramics.

The concept of high-entropy materials (HEMs) finds its roots in high-entropy alloys (HEAs), which are multi-principal element alloys (MPEAs) characterized by an equal or near-equal atomic fraction of constituent elements (Cantor et al., 2004; Rajendrachari, 2022b). The distinction between HEAs and traditional alloys extends beyond properties and their design strategy. In traditional alloy design, a single base element, for instance, Fe, Mg or Ti, serves as the principal element, with minor alloy elements added to enhance properties, following the “base element concept” (Zhang et al., 2014). In contrast, the HEA design strategy involves mixing five or more multi-principal elements into a single lattice, creating a solid solution (Kale et al., 2022). In phase diagrams, traditional alloy compositions are generally found at the corners, limiting compositional design space. At the same time, HEAs occupy the central region, significantly expanding the design space through the combination of multi-principal elements and microstructures (Cantor, 2014).

Inspired by the breakthroughs in the field of metals, the high-entropy concept has been extended to composites (HECos), polymers (HEPs) and ceramics (HECs). Like HEAs, all high-entropy materials are characterized by long-range structural order but compositional disorder. However, high-entropy ceramics (HECs) offer more opportunities for tuning properties and addressing material application challenges. Ceramics boast diverse crystal structures beyond the simple FCC, BCC, and HCP structures found in metals (Sharma, Yadav, Biswas et al, 2018). Moreover, the variety in band structure and chemical bonding in ceramics opens new avenues for material design and property tuning through band structure and phonon engineering. HECs, with their numerous possibilities in composition design and property tuning paradigms, have demonstrated improved stability, enhanced mechanical properties, thermal conductivity (Braun et al., 2018) and potential in various functional and structural applications, ranging from ultrahigh-temperature thermal protection and insulation in hypersonic vehicles to thermal/environmental barrier protection of engine materials, high-speed and dry cutting, Li-ion batteries, thermoelectrics, and electromagnetic wave absorption & interference shielding (Chen, Xiang, Dai, Liu, Lei et al, 2019).

Despite rapid development, the field of HECs is still in its early stages, both in terms of academic research and practical applications. Additionally, the novel design concept and the underlying mechanisms responsible for these unusual phenomena present theoretical and experimental challenges.