Chunlei Wan

Thermoelectric (TE) materials, capable of directly converting waste heat into electricity and enabling solid‐state cooling, hold great potential for self‐powered microelectronics and miniature sensors in the Internet of Things (IoT) and wearable technologies. Two‐dimensional (2D) MoS ₂ (molybdenum disulfide) stands out as a promising candidate due to its compatibility with CMOS (Complementary Metal Oxide Semiconductor) back‐end‐of‐line processes, which are well‐established in microelectronics fabrication. It is experimentally suggested that bilayer MoS ₂ exhibits an ultra‐high‐power factor ( PF ) of 85 µW cm ⁻¹ K ⁻² , which is attributed to its optimized electronic band structure and higher density of states near the Fermi level ( E _F ). However, experimental figure of merit ( zT ) values for most MoS ₂ ‐based mesoscale materials still remain low, typically below 0.2 near room temperature, due to the intrinsic high thermal conductivity of 2D MoS ₂ and uncontrolled dimensionality in MoS ₂ bulks. This review summarizes recent advances in the methods for preparing the MoS ₂ ‐based TE materials and the strategies for tuning the TE performance of MoS ₂ through doping, intercalation, hetero‐structuring, and unique microstructure optimization strategies. In the end, current challenges and future perspectives regarding the further improvement of zT values for MoS ₂ and the commercialization of CMOS‐compatible, high‐performance MoS ₂ ‐based TE devices are discussed.

Traditional YSZ coatings are approaching their temperature limits, leading to extensive research focused on developing new thermal barrier coating materials. GAO–GZO has emerged as a potential candidate to replace YSZ due to its excellent thermodynamic properties. The GAO–GZO/YSZ dual‐layer coating structure has also demonstrated outstanding thermal cycling lifetime. However, the stability of the structure and performance of GAO–GZO coatings at high temperatures remain questionable. Therefore, we fabricated freestanding GAO–GZO coatings using atmospheric plasma spraying and investigated the evolution of their structure and properties at 1300°C. Our study found that after heat treatment at 1300°C, the GAO–GZO coating transformed from a single phase to a multiphase structure, with reduced internal defects and a significant decrease in porosity. These structural changes resulted in a substantial increase in thermal conductivity by 68.4% at 1000°C after sintering at 1300°C for 100 h, while having a minor impact on the coefficient of thermal expansion.

The pursuit of oxidation‐resistant materials for temperatures exceeding 2500°C is fundamentally bottlenecked by the melting points of oxide ceramics. While maximizing cohesive enthalpy has been the traditional route, this approach has reached its thermodynamic limit. Herein, we report a paradigm shift by deliberately engineering entropy—the long‐overlooked variable in melting‐point control. Using the model system Lu _x Hf _1‐x O _2‐0.5x , we demonstrate that oxygen vacancies act as a potent “entropy lever.” Their introduction creates disorder on the anion sublattice, which selectively amplifies the solid's configurational entropy without equivalently raising the liquid's entropy, while simultaneously driving the solid's local bonding environments closer to those of the liquid and reducing their vibrational entropy difference. This synergistic effect drastically lowers the entropy of fusion, resulting in a record‐high melting point of ∼2912°C at an optimal composition (x ≈ 0.4). This work establishes entropy‐mediated design, realized through defect engineering, as a transformative strategy to break the long‐standing melting‐point ceiling in ultra‐high‐temperature oxide ceramics.

Silicon carbide fiber–reinforced silicon carbide (SiC _f /SiC) composites are promising candidates for advanced gas turbines owing to their low density and excellent high‐temperature strength. However, their service temperature is severely limited by oxidation and corrosion in water vapor–rich environments, necessitating the use of environmental barrier coatings (EBCs). Conventional EBCs, such as rare‐earth silicates, provide effective protection up to 1300–1400°C but degrade rapidly above 1500°C due to crystallization of SiO ₂ ‐based thermally grown oxides and phase instability. Consequently, robust outer‐layer materials compatible with inner‐layer EBCs are required for multilayer T/EBC systems operating under severe conditions. In this work, perovskite‐type rare‐earth oxides LaYbO ₃ and LaY _1/2 Yb _1/2 O ₃ are evaluated as candidate outer‐layer T/EBC materials for SiC composites and are found to exhibit thermal expansion coefficients of 7.0–8.5 × 10 ^{− 6} K ^{− 1} , supporting their suitability for such applications. Their low thermal conductivity (≤1.8 W m ^{− 1} K ^{− 1} ) provides effective thermal insulation, while their relatively high hardness and fracture toughness contribute to improved mechanical integrity. These results indicate that perovskite‐type rare‐earth oxides are promising outer‐layer T/EBC materials for enhancing the durability of SiC‐based components under ultra‐high‐temperature conditions.

Two-dimensional (2D) materials, including graphene and MXenes, have garnered significant interest for enhancing both the mechanical and multifunctional properties of advanced structural ceramics. These materials encounter operational limitations under high temperatures, particularly due to oxidative degradation of 2D reinforcement architectures that induces composition instability and property deterioration. In this study, we developed a processing methodology for fabricating 2D Al₂O₃ platelet-reinforced yttria-stabilized zirconia (YSZ) composites, which can be stable up to 1300 ^oC in an atmosphere. Through a multi-field coupling strategy combining gravitational field modulation, high-intensity vibrational alignment, and controlled pressure densification, we achieved densified composites with parallel-aligned Al₂O₃ platelet array in YSZ matrix. The composite demonstrates reduced near-infrared (NIR) transmittance below 10%, effectively blocking radiative thermal transfer. Meanwhile, The YSZ-Al₂O₃ platelet composite (YSZ-Al₂O₃-PL) simultaneously demonstrates enhanced resistance to CaO-MgO-AlO_1.5-SiO₂ (CMAS) molten salts and improved fracture toughness. The cost-effective 2D oxide/ceramic composites possess exceptional thermo-mechanical stability, promising for harsh environments.

Achieving high and stable permittivity is essential for developing ultra‐thin and wide‐temperature adaptive microwave‐absorbing materials (MAMs). Conventional high‐permittivity MAMs suffer from temperature‐sensitive permittivity and cannot achieve stable microwave‐absorbing performance at fluctuating temperatures, while temperature‐insensitive MAMs exhibit low permittivity that severely restricts ultra‐thin designs. Herein, a double‐layer La ₂ Zr ₂ O ₇ /Eu ₂ Zr ₂ O ₇ architecture is employed, with rare‐earth zirconates featuring with one‐eighth anion‐site vacancies, as a promising candidate for ultra‐thin wide‐temperature adaptive MAMs. The established balance between thermionic relaxation polarization and Lorentz dielectric resonance—activated by oxygen ions—can largely increase the real part of permittivity of La ₂ Zr ₂ O ₇ while maintaining its stability at different temperatures. Concurrently, strong thermionic transport induces an increase in dielectric loss capacity of Eu ₂ Zr ₂ O ₇ , which can broaden effective absorption bandwidth (EAB) effectively. Moreover, the macroscopic interfacial resonance between two layers overcomes the limitations imposed by the quarter‐wavelength theory, generating new absorption peak for further expanding EAB. Under synergistic coupling of these mechanisms, it is successfully achieved superior EAB—completely covering the Ku band (12.4–18 GHz) over a wide‐temperature range (400–800 °C) at an ultra‐thin fixed thickness of just 1.2 mm, coupled with a maximum EAB/ d of 3.6 GHz mm ⁻¹ . This innovative design offers promising pathways for developing ultra‐thin and wide‐temperature adaptive MAMs.

Rare‐earth zirconates (REZO) have emerged as next‐generation thermal barrier coating materials, owing to their exceptional phase stability, ultralow high‐temperature thermal conductivity, and high thermal expansion coefficient. However, their relatively low fracture toughness limits practical implementation. While numerous studies have documented fracture toughness measurements in REZOs at room temperatures, the intrinsic influences of rare‐earth element selection and order‐disorder phase transitions on fracture mechanisms at various temperatures remain insufficiently explored. This study integrates molecular dynamics simulations with high‐throughput calculations and experimental validation to systematically elucidate how rare‐earth cation configurations, crack propagation orientations, and order‐disorder transition govern fracture toughness and crack evolution in REZO systems. Our findings demonstrate brittle fracture behavior across all crystallographic orientations in REZOs, with maximum critical stress along (100) and minimum along (111). Fracture characteristics correlate not only with surface energy but also with geometric factors at crack tips. Molecular dynamics simulations reveal that structural disorder reduces fracture toughness without altering failure mechanisms. The integration of experimental and computational analyses for Nd ₂ Zr ₂ O ₇ demonstrates that REZO exhibits lattice softening and reduced fracture toughness at elevated temperatures while maintaining brittle fracture characteristics. These findings establish critical experimental and theoretical foundations for advancing high‐toughness, long‐lifespan REZO‐based thermal barrier coating materials.

The escalating demand for long-term high-temperature microwave-absorbing materials (HTMAMs) in high-speed aerospace stealth is hindered by limitations such as magnetic loss degradation or oxidation risks. Herein, we introduce rare earth zirconate ceramics that exhibit air stability up to 1600 °C. Abundant oxygen vacancies significantly enhance permittivity and thus microwave-absorbing performance through activated thermionic migration at elevated temperatures. Moreover, the thermionic-facilitated permittivity can be meticulously modulated by electron delocalization, with the extent governed by lattice disorder. We demonstrate this concept through a dual-layer Er₂Zr₂O₇/Gd₂Zr₂O₇ structure to further optimize impedance matching, achieving an ultra-wide bandwidth (8.27 GHz) and strong absorption (−64.61 dB) at ultrathin thicknesses under 1.2 mm at 600 °C mainly by macroscopic interfacial resonance, alongside an ultralow thermal conductivity (1.61 W•m^-1•K^-1). This work presents an innovative approach to design high-performance and anti-oxidative HTMAMs through thermionic migration tuned by electron delocalization, advancing structural-functional integrated materials for extreme environments.

To meet gas turbines’ growing demand for high-performance thermal barrier coatings (TBCs), this study addresses the limitations of traditional single-layer 8% Y₂O₃-stabilized ZrO₂ (YSZ) coatings in high-temperature corrosive environments. Atmospheric plasma spraying (APS) was used to fabricate the double-ceramic TBCs with (Sm_0.2Gd_0.2Dy_0.2Er_0.2Yb_0.2)₂(Zr_0.7Hf_0.3)₂O₇ (RHZ) as the outer layer and YSZ as the inner layer; thermal cycling corrosion tests (1000 °C, Na₂SO₄ + V₂O₅ molten salt) were conducted to compare its performance with traditional single-layer YSZ. The results showed that the YSZ corrosion products were m-ZrO₂ and YVO₄, while RHZ/YSZ produced rare-earth vanadates, m-(Zr,Hf)O₂, and t′-(Zr,Hf)O₂, and corrosion degree was positively correlated with salt concentration (which was more impactful) and the number of cycles. Both coatings failed via molten salt penetration, thermochemical reaction, and crack-induced spallation. The corrosion mechanism between the RHZ/YSZ coating and the mixed salt can be explained based on the Lewis acid–base theory and the optical basicity. The RHZ layer on the surface of RHZ/YSZ coatings indeed hinders the penetration of corrosive molten salts into the underlying YSZ layer to some extent.