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High-entropy ceramics (HECs) are a class of ceramic materials composed of multiple principal elements, typically four or more cations and/or anions, that form a single-phase solid solution stabilized in part by high configurational entropy. The concept is derived from high-entropy alloys, but high-entropy ceramics differ fundamentally in bonding, crystal chemistry, and functional behavior. Since the first experimental demonstration of entropy stabilization in oxides in 2015,^[1] high-entropy ceramics have expanded to include oxides, carbides, nitrides, borides, silicides, and chalcogenides, attracting interest for structural and functional applications such as thermal barrier coatings, energy storage, catalysis, and thermoelectrics.^[2][3]

While oxides were the first ceramic systems in which entropy stabilization was experimentally demonstrated, the concept has since been extended well beyond oxides to strongly covalent and refractory ceramic materials.^[2][3][4]

High-entropy ceramics are generally defined as single-phase ceramic compounds containing no fewer than four distinct elements on at least one crystallographic sublattice, often in near-equimolar ratios.

The stabilization of high-entropy ceramics is commonly rationalized by the Gibbs free energy expression:${\displaystyle \Delta G=\Delta H-T\Delta S}$, where G is Gibbs free energy, H is enthalpy, T is absolute temperature, and S is entropy. Moreover, the configurational entropy term increases with the number of constituent elements. For an ideal equimolar solid solution containing N components, the configurational entropy is given by ${\displaystyle \Delta S_{config}=R\ln N}$. At sufficiently high temperatures, this entropy contribution can overcome positive mixing enthalpies and favor the formation of simple crystal structures such as rock-salt, fluorite, or perovskite lattices.

Unlike high-entropy alloys, which are metallically bonded, high-entropy ceramics typically exhibit ionic or covalent bonding. In many cases, an ordered anion sublattice (e.g., O²⁻, N³⁻, C⁴⁻, B³⁻) accommodates a highly disordered cation sublattice, reducing elastic and electrostatic penalties associated with size and charge mismatch. This structural feature plays a crucial role in enabling entropy stabilization in ceramic systems.

High-entropy ceramics have been reported in a wide variety of crystal structures, including rock-salt,^[1] fluorite,^[5] perovskite,^[6] spinel,^[7] and hexagonal lattices. Beyond oxides, major material classes include: High-entropy carbides,^[8][9][10] High-entropy nitrides^[11], High-entropy borides^[12] and silicides,^[13][14] and High-entropy chalcogenides.^[15]

Different types of High entropy ceramics and their properties

High-entropy ceramics are typically synthesized using high-temperature processing routes to promote atomic-scale mixing of multiple principal elements and suppress phase separation. Because configurational entropy contributes significantly to phase stability at elevated temperatures, most synthesis methods involve heating to activate diffusion, followed by controlled cooling to retain single-phase structures at room temperature.

Solid-state reaction methods^[2][16] are widely used for bulk high-entropy ceramics. In this approach, precursor powders are mixed in near-equimolar ratios and sintered at high temperatures to form homogeneous solid solutions. For non-oxide systems such as carbides and borides, solid-state synthesis is often combined with carbothermal or borothermal reduction reactions.

Mechanochemical processing,^[17][18][19]frequently followed by spark plasma sintering or hot pressing, has been employed to reduce synthesis temperatures and processing times. High-energy ball milling enhances reactivity and diffusion, enabling the formation and densification of high-entropy carbides and borides with refined microstructures.

Wet-chemical routes,^[20][21][22]including sol–gel and co-precipitation methods, are primarily applied to high-entropy oxides, where molecular-level mixing of cations can be achieved prior to crystallization. These methods generally produce fine and chemically homogeneous powders.

Thin-film high-entropy ceramics are commonly synthesized by physical vapor deposition techniques such as magnetron sputtering and pulsed laser deposition,^[23][24] which allow precise compositional control and can stabilize metastable high-entropy phases suitable for coating applications.

High-entropy ceramics exhibit a range of properties influenced by lattice distortion, chemical disorder, and sluggish diffusion:

• Mechanical properties: enhanced hardness, strength, and resistance to grain growth^[25][26]
• Thermal properties: low thermal conductivity resembling amorphous materials^[27]
• Chemical stability: resistance to oxidation and corrosion at high temperatures^[27]
• Electrical and ionic transport: tunable conductivity and superionic behavior in selected systems^[28]
• Magnetic and electronic properties: complex magnetic ordering and adjustable band gaps^[29][30]

Potential and demonstrated applications of high-entropy ceramics include:

High-entropy ceramics have been investigated as candidate materials for energy storage applications, particularly in electrochemical systems. High-entropy oxides have been studied as electrode materials and solid electrolytes in rechargeable batteries, where the incorporation of multiple cation species can stabilize single-phase crystal structures over wide compositional ranges. Chemical disorder and lattice distortion in these materials may influence ionic transport behavior and structural stability during repeated electrochemical cycling. As a result, high-entropy ceramics are being explored in lithium-ion, sodium-ion, and other emerging battery systems, as well as in solid-state energy storage technologies.^{[31][32][33][34]}

High-entropy ceramics have also been explored for thermoelectric applications, where materials with low thermal conductivity and suitable electrical transport properties are required. The presence of multiple elements with different atomic masses and bonding characteristics leads to strong phonon scattering, which can reduce lattice thermal conductivity. At the same time, electrical properties can be adjusted through compositional design and doping. High-entropy oxides and chalcogenides have been reported to exhibit reduced thermal transport and tunable electronic behavior, suggesting that entropy-based compositional strategies may be useful in the development of ceramic thermoelectric materials, particularly for high-temperature operation.^[35]

High-entropy ceramics have been investigated for use in thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) due to their phase stability and chemical robustness at elevated temperatures. The presence of multiple constituent elements can suppress phase transformations and reduce thermal conductivity through enhanced phonon scattering, which is desirable for thermal insulation. In addition, certain high-entropy ceramic compositions exhibit improved resistance to oxidation, corrosion, and water-vapor attack, making them of interest for protective coatings on turbine components and ceramic matrix composites operating in harsh environments.^[36][37][38]

High-entropy ceramics have also been explored as wear- and corrosion-resistant coatings, particularly in the form of nitrides, carbides, and oxides deposited as thin films. The chemical disorder and lattice distortion inherent to high-entropy systems can enhance hardness and inhibit grain growth, contributing to improved wear resistance. In corrosive environments, the presence of multiple alloying elements may promote the formation of stable passivation layers and reduce elemental diffusion, leading to improved corrosion resistance. These properties have motivated research into high-entropy ceramic coatings for cutting tools, mechanical components, and protective surface layers.^{[39][40][41][42][43]}

High-entropy ceramics have been studied as catalyst materials for reactions such as oxidation, hydrogenation, and water splitting. The incorporation of multiple cation species can generate a wide distribution of local chemical environments and active sites, which may influence catalytic activity and selectivity. In oxide-based systems, compositional complexity can also enhance thermal stability and resistance to deactivation under reaction conditions. As a result, high-entropy ceramics are being examined as catalyst supports or active materials in heterogeneous catalysis and energy-related chemical processes.^[44][45][46]

• High entropy oxide
• High entropy alloy