A five-element ceramic aerogel compresses by 98% and recovers its shape from cryogenic to 1500 degrees C temperatures, outperforming conventional thermal insulation materials.
(Nanowerk Spotlight) Ceramic aerogels occupy a peculiar niche in materials science: they are among the lightest solid materials ever created, yet they must withstand conditions that would destroy almost anything else. These ultralight structures, riddled with billions of nanoscale pores, can block heat transfer with extraordinary efficiency. This makes them indispensable for insulating spacecraft during atmospheric reentry, protecting gas turbines operating at blistering temperatures, and shielding hypersonic aircraft traveling at extreme speeds.
But ceramics have an inherent problem. The same rigid atomic bonds that give them heat resistance also make them brittle, prone to shattering under mechanical stress or thermal shock. Worse, at extreme temperatures, their crystalline grains grow larger, destroying the delicate porous architecture that makes aerogels useful in the first place.
Engineers have searched extensively for ceramic materials that can remain mechanically flexible while retaining thermal stability, a combination that has proved extraordinarily difficult to achieve with conventional single-element oxides like aluminum oxide, zirconium oxide, or silicon carbide.
A relatively new class of materials called high-entropy ceramics offers a potential solution. Unlike traditional ceramics made from one or two metal elements, high-entropy ceramics incorporate five or more different metal atoms arranged randomly on the same crystalline lattice sites. This chaotic atomic arrangement produces unusual properties. The lattice becomes severely distorted because atoms of different sizes must squeeze together, which scatters heat-carrying vibrations called phonons and dramatically reduces thermal conductivity. The atomic disorder also creates thermodynamic stability at high temperatures and suppresses the diffusion that normally causes grain growth.
Now, a research team based primarily at the Lanzhou Institute of Chemical Physics in China has created a high-entropy oxide ceramic aerogel that achieves this elusive combination of properties. In a study published in the journal Advanced Science (“Superelastic High‐Entropy Oxide Ceramic Aerogels for Thermal Superinsulation and Sealing at Extreme Conditions”), the researchers describe a material composed of five metal elements: gadolinium, lutetium, titanium, zirconium, and hafnium, combined with oxygen in a specific crystalline arrangement.
The resulting aerogel exhibits what the researchers describe as superelastic compressibility. It can be compressed by 98% and spring back to its original shape across a temperature range spanning from −196 °C to 1500 °C. Its thermal conductivity measures just 24.14 mW·m⁻¹·K⁻¹ at room temperature and 81.21 mW·m⁻¹·K⁻¹ at 1000 °C, values that outperform most existing ceramic insulation materials at high temperatures.
The schematic illustration of conceptual formation for high-entropy oxide-based ceramic aerogels, including metal cation selection, proportion optimization, the crystal design, the acetylacetone complex synthesis, the solid-solution reaction, and 3D aerogel monolith stacking. (Image: Reproduced from DOI:10.1002/advs.202516840, CC BY) (click on image to enlarge)
The researchers synthesized their material, abbreviated as GLTZH from the chemical symbols of its constituent elements (Gd, Lu, Ti, Zr, Hf), through a molecular-level approach rather than traditional ceramic processing. Conventional high-entropy ceramics typically require grinding oxide powders together and heating them to extreme temperatures, a process that can introduce impurities and uneven element distribution.
The team instead created polymer-like precursor molecules for each of the five metals, then mixed these precursors in precise ratios. When heated, these precursors decompose and react, spontaneously forming a perfectly mixed atomic arrangement where all five metal types occupy lattice positions randomly. This molecular synthesis route eliminates the grain boundary impurities and compositional segregation that plague ball-milled powders.
The team selected their five elements based on the Hume-Rothery criterion, a set of rules predicting which metals can dissolve into each other to form stable alloys. Gadolinium and lutetium, both rare-earth elements, occupy one type of crystalline site, while titanium, zirconium, and hafnium occupy another.
The ionic radii of these elements span a moderate range, from about 0.745 Å for titanium to 1.053 Å for gadolinium. This size variation creates local lattice distortion necessary for enhanced phonon scattering while still permitting formation of a single stable phase. Molecular dynamics simulations confirmed that this particular combination exhibited the lowest potential energy and greatest thermodynamic stability among the alternative compositions tested.
Using atomic-resolution electron microscopy, the researchers traced how their precursor transforms into crystalline ceramic at temperatures from 200 °C to 1100 °C. Below 200 °C, the material remains amorphous. Between 400 °C and 600 °C, tiny crystalline nuclei begin forming. Above 800 °C, a highly ordered structure emerges.
Crucially, even after two hours at 1400 °C, the average grain size remained around 247 nm, far smaller than the 625 nm grains observed in pure zirconium oxide processed identically. The team fabricated their aerogel using electrospinning, a technique that uses electric fields to draw polymer solutions into extremely thin fibers. They collected the resulting nanofibers and heated them to 1000 °C.
The finished aerogel consists of a three-dimensional network of fibers averaging 250 nm in diameter, with spacing of about 5 μm between layers. Strong bonds at fiber junctions reinforce the structure against mechanical stress. The material achieves a density of just 4.35 mg/cm³, light enough to rest on flower petals.
Mechanical testing revealed remarkable resilience. The aerogel withstood 1000 compression cycles at 50% strain without structural failure, tolerated 360-degree torsion and 180-degree bending, and recovered fully from compression in liquid nitrogen. The researchers also demonstrated that the material could be compressed flat while exposed to an acetylene torch flame at approximately 1300 °C, then recover its original shape once released.
The researchers attribute this stability to effects inherent to high-entropy materials: severe lattice distortion that impedes heat-carrying vibrations, suppressed atomic diffusion that prevents grain growth, and thermodynamic stabilization from the high configurational entropy of five randomly mixed elements. Titanium, despite forming the lowest-melting oxide among the five components, helps suppress infrared radiation at high temperatures, an important contribution to thermal insulation.
This work demonstrates that the counterintuitive atomic disorder of high-entropy materials can solve a fundamental engineering problem. By combining five carefully selected elements through molecular-level synthesis and nanofiber architecture, the researchers created a ceramic that defies the traditional trade-off between mechanical compliance and thermal stability.
The material’s ability to function from cryogenic temperatures to 1500 °C, while maintaining both flexibility and insulating capacity, could enable next-generation thermal protection for hypersonic vehicles, advanced turbines, and aerospace applications where conventional ceramics fail.
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