Tikalon Header Blog Logo

High Entropy Ceramics

February 26, 2024

One principle that scientists and engineers learn is the difference between the ideal and the actual. Unfortunately, the difference is learned mostly in the prolonged process of discovery of why your circuit or experiment is not giving the anticipated response. Electrical resistance changes with temperature, materials expand and contract, and that ideal amplifier you're using has noise, limited frequency response, and a significantly small input impedance. Eventually, one learns to anticipate such problems, and computer simulations are now available as a design aid.

An ideal elemental metal is a perfect crystal; but, just melting and solidifying a metal does not give you a huge single crystal. Instead, you get a lump of polycrystals, and the physical properties of that lump are not just dependent on the metal, but also the microstructure of the solid. When making an alloy, a liquid mixture of several different types of metals will give you a polycrystalline solid consisting of multiple crystal phases when solidified. The crystal phases present in an alloy and their relative concentrations can be used to increase its strength by limiting the movement of dislocations.

As I wrote in a previous article (High-Entropy Alloys, June 20, 2016), multiple metals can be combined to make an alloy with just a single phase. In 2014, materials scientists at Oxford University produced a single phase alloy of equal portions of five elements.[1] This alloy was a face-centered cubic solid solution with composition Fe20Cr20Mn20Ni20Co20. Such a material is known as a high entropy alloy.

atomic structure model of FeCrMnNiCo

Atomic structure model of the Oxford University Fe20Cr20Mn20Ni20Co20 alloy.

In this image, magenta = Fe, green = Co, blue = Cr, cyan = Ni, and yellow = Mn. Aside from slight differences in atomic size, swapping colors would serve just as well, since the composition has equal numbers of each element.

(Image by Shaoqing Wang, via Wikimedia Commons.)

Do high entropy alloys have any properties that are especially useful? High entropy alloys have been shown to have better radiation resistance.[2] Now that fossil fuel energy is being replaced by other technologies, their potential for use in nuclear reactors could become important. Energetic particles, such as neutrons, cause displacement of atoms from their positions in the crystal lattice upon impact and produce lattice defects and dislocations that affect the alloy's mechanical properties. The peculiar structure of a high-entropy alloy diminishes the severity of defect formation.

High entropy ceramics are a companion material type of high entropy alloys, and they have radiation resistant properties as well. The first studied classes of these HECs are the high entropy carbides (HECs) and oxides (HEOs).[3] Such ceramics can exhibit better stability at high temperature, better corrosion resistance, and significantly higher hardness, than metallic alloys.[3] Early studies of HECs have reported that radiation effects, such as void formation, amorphization, and radiation-induced segregation do not occur.[3] One high entropy carbide, (CrNbTaTiW)C, demonstrated considerable radiation immunity.[3] This carbide was not amorphized under radiation dosage conditions at which high entropy alloys are likewise unaffected.[3]

Radiation resistance of the high entropy carbide, (CrNbTaTiW)C, compared with a high entropy alloy at the same radiation dosage

Radiation resistance of the high entropy carbide, CrNbTaTiW)C, compared with a high entropy alloy at the same radiation dosage. The histograms show the average diameter of bubbles formed from xenon irradiation at the same dosage of 10 displacements-per-atom. (A portion of fig 4 of ref. 3,[3] released under a Creative Commons license.)

High-entropy carbides were discovered in 2018.[4-5] Now a research team from Duke University (Durham, North Carolina), Penn State University (State College, Pennsylvania, the Missouri University of Science and Technology (Rolla, Missouri), North Carolina State University (Raleigh, North Carolina)y, and the State University of New York at Buffalo (Buffalo, New York) has developed a method, called a disordered enthalpy–entropy descriptor (DEED), that aids the discovery of synthesizable multicomponent ceramics.[4] DEED assists in experimental discovery of single phase high entropy carbonitrides and borides with a focus on the use of sintering by hot isostatic pressing.[5] In sintering by hot isostatic pressing, powders of the constituent compounds of the ceramic are heated in a vacuum at high temperature and pressure for many hours.[5]

The DEED method has already predicted 900 new synthesizable ceramics, seventeen of which have been prepared and analyzed.[5] The ceramics synthesized by this sintering process are dark grey or black, and they have a density close to that of a metal alloy; however, they are hard and brittle as are other ceramics.[5] The Duke University research team maintains a materials database called the Duke Automatic-FLOW for Materials Database (AFLOW) that offer data for simulation methods such as DEED.[6] AFLOW even contains data on an exotic material, HfPt3 investigated by some of my graduate school colleagues in the 1970s. This research was funded by United States Department of Defense Multidisciplinary University Research Initiative (MURI), and the United States Department of Defense High Performance Computing Modernization Program (HPC-Frontier).[5]

Ludwig Boltzmann (1844-1906)

The description of entropy as a function of the number of microstates possible in an ideal gas was discovered by Austrian physicist, Ludwig Boltzmann (1844-1906), in 1877. His famous equation, now written as S = kBln(Ω), in which S is the entropy, kB is the Boltzmann constant, and Ω is the number of microstates, appears on his grave marker at the Central Cemetery in Vienna, Austria. (Left image, and right image, both from Wikimedia Commons. Click for larger image.)


  1. B. Cantor, I.T.H. Chang, P. Knight, and A.J.B. Vincent, "Microstructural development in equiatomic multicomponent alloys," Materials Science and Engineering, vols. 375-377 (July 2004), pp. 213-218, doi:10.1016/j.msea.2003.10.257.
  2. O. El-Atwani, N. Li, M. Li, A. Devaraj, J. K. S. Baldwin, M. M. Schneider, D. Sobieraj, J. S. Wróbel, D. Nguyen-Manh, S. A. Maloy, and E. Martinez, "Outstanding radiation resistance of tungsten-based high-entropy alloys," Science Advances, vol. 5, no. 3 (March 1, 2019), DOI: 10.1126/sciadv.aav2002.
  3. Matheus A. Tunes, Stefan Fritze, Barbara Osinger, Patrick Willenshofer, Andrew M. Alvarado, Enrique Martinez, Ashok S. Menon, Petter Strö, Graeme Greaves, Erik Lewin, Ulf Jansson, Stefan Pogatscher, Tarik A. Saleh, Vladimir M. Vishnyakov, and Osman El-Atwani, "From high-entropy alloys to high-entropy ceramics: The radiation-resistant highly concentrated refractory carbide (CrNbTaTiW)C," Acta Materialia, vol. 250 (May 15, 2023), Article no. 118856, https://doi.org/10.1016/j.actamat.2023.118856. This is an open source article with a PDF file available at the same URL.
  4. Simon Divilov, Hagen Eckert, David Hicks, Corey Oses, Cormac Toher, Rico Friedrich, Marco Esters, Michael J. Mehl, Adam C. Zettel, Yoav Lederer, Eva Zurek, Jon-Paul Maria, Donald W. Brenner, Xiomara Campilongo, Suzana Filipović, William G. Fahrenholtz, Caillin J. Ryan, Christopher M. DeSalle, Ryan J. Crealese, Douglas E. Wolfe, Arrigo Calzolari, and Stefano Curtarolo, "Disordered Enthalpy-Entropy Descriptor for High-Entropy Ceramics Discovery," Nature, vol. 625, no. 7993 (January 4, 2024), pp. 66-73DOI: 10.1038/s41586-023-06786-y. This is an open source article with a PDF file available at the same URL.
  5. Computational method discovers hundreds of new ceramics for extreme environments, Duke University Press Release, January 3, 2024.
  6. AFLOW Website, Center for Autonomous Materials Design, Materials Science, Duke University.

Linked Keywords: Principle; scientist; engineer; theory of forms - ideal state; ideal; reality; actual; electronic circuit; experiment; expectation (epistemic); anticipated response; electrical resistance; temperature; material; thermal expansion; expand and contract; amplifier; noise (electronics); frequency response; electrical impedance; input impedance; computer simulation; design; chemical element; elemental; metal; single crystal; perfect crystal; melting; freezing; solidifying; lump; crystallite; polycrystal; physical property; dependent variable; microstructure; solid; alloy; liquid; mixture; polycrystalline; phase (matter); concentration; strength of materials; dislocation; materials science; materials scientist; University of Oxford; Oxford University; cubic crystal system; face-centered cubic; solid solution; empirical formula; Iron; Fe; Chromium; Cr; Manganese; Mn; Nickel; Ni; Cobalt; Co; high entropy alloy; space-filling model; atomic structure model; atomic radius; atomic size; chemical element; radiation damage; radiation resistance; fossil fuel; energy; technology; technologies; nuclear reactor; energy; energetic; subatomic particle; neutron; displacement (vector); crystal structure; crystal lattice; impact (mechanics); crystallographic defect; lattice defect; mechanical properties; high entropy oxide; high entropy ceramic; categorization; class; carbide; oxide; corrosion resistance; hardness; research; study; porosity; void formation; amorphous solid; amorphization; segregation (materials science); carbide; Niobium; Nb; Tantalum; Ta; Titanium; Ti; Tungsten; W; Carbon; C; entropy; radiation dosage; histogram; diameter; bubble; xenon; irradiation; Creative Commons license; Duke University (Durham, North Carolina); Penn State University (State College, Pennsylvania; Missouri University of Science and Technology (Rolla, Missouri); North Carolina State University (Raleigh, North Carolina); State University of New York at Buffalo (Buffalo, New York); enthalpy; chemical synthesis; synthesizable; carbonitride; boride; sintering; hot isostatic pressing; powder (substance); vacuum; pressure; hour; analysis; analyze; density; brittleness; brittle; database; computer simulation; simulation method; exotic; HfPt3; graduate school; colleague; 1970s; funding of science; funded; United States Department of Defense; Multidisciplinary University Research Initiative (MURI); High Performance Computing Modernization Program (HPC-Frontier); function (mathematics); microstate (statistical mechanics); ideal gas; Austria; Austrian; physicist; Ludwig Boltzmann (1844-1906); Boltzmann constant; headstone; grave marker; Vienna, Austria.