From high-entropy ceramics to compositionally complex ceramics and beyond

Over the past decade, the field of high-entropy ceramics (HECs) has expanded rapidly to encompass a broad range of oxides, borides, silicides, and other ceramic solid solutions. In 2020, we proposed extending HECs to compositionally complex ceramics (CCCs), where non-equimolar compositions and the presence of long- or short-range order, although reducing configurational entropy, create new opportunities to tailor and enhance properties, often surpassing those of higher-entropy counterparts. Along these lines, several fundamental scientific questions arise. Is the entropy in HECs truly high? Is maximizing entropy always desirable? In this perspective article, I revisit key concepts and terminologies and highlight emerging directions, including dual-phase CCCs, ultrahigh-entropy phases, and novel processing routes such as ultrafast reactive sintering. I propose that exploring compositional complexity across vast non-equimolar spaces, together with correlated disorder (coupled chemical and structural short-range order), offers a groundbreaking strategy for designing ceramics with superior performance. • High-entropy ceramics (HECs) have rapidly expanded across diverse chemistries, crystal structures, and bonding characters. • HECs extend to compositionally complex ceramics (CCCs), where lower-entropy CCCs can outperform higher-entropy ones. • Non-equimolar designs offer additional freedom to tune and enhance material properties. • Short-range order (correlated disorder) in CCCs can enable superior properties. • Dual-phase CCCs and innovative processing methods, such as ultrafast reactive sintering, open new research directions.