From High-Entropy Ceramics (HECs) to Compositionally Complex Ceramics (CCCs) and Beyond

Abstract: Over the past decade, the field of high-entropy ceramics (HECs) has rapidly expanded to encompass a wide range of oxides, borides, silicides, and other ceramic solid solutions. In 2020, we proposed extending the concept of HECs to compositionally complex ceramics (CCCs), in which non-equimolar compositions and the presence of long- or short-range order reduce entropy while offering new opportunities to tailor and enhance properties, often beyond those of higher-entropy counterparts. Here, fundamental questions arise: Is the entropy in HECs truly high? Should maximizing entropy always be our goal? This perspective article revisits key concepts and terminologies and highlights emerging directions, including dual-phase CCCs, ultrahigh-entropy phases, and novel processing routes such as ultrafast reactive sintering. We propose that exploring compositional complexity across vast non-equimolar spaces, together with correlated disorder (coupled short-range chemical and structural orders), offers a more effective strategy for designing ceramics with superior performance than simply maximizing entropy.