Design and synthesis of chemically complex ceramics from the perspective of entropy

High-entropy ceramics (HECs) have rapidly expanded from high-entropy oxides to high-entropy ultrahigh temperature ceramics/coatings and have drawn extensive attention in the field of ceramics. In addition, high-entropy thermoelectric materials focus on the topic of energy, which is another major driving force to accelerate the development of HECs. In this review, the recent progress on the design and synthesis of chemically complex ceramics is summarized. The fundamental understanding of configurational entropy, phase stability, and formation criterion of HECs are discussed. Critical comments on the compositionally complex ceramics and mixed-valence complex ceramics are presented. The synthesis methods of HECs are summarized, and reactive flash sintering is highlighted as a new strategy to synthesize HECs. The new design ideas and synthesis methods can provide more opportunities to develop high-performance HECs to meet the requirements of cutting-edge applications.