WANG Shuo, LU Junyang, ZHANG Tong, FANG Zhenhan, ZHENG Jiayi, ZHANG Mengqing

(Research Institute of Chemical Defense, Beijing 102205, China)

Extended abstract:[Significance] With the rapid development of laser technology, there is an urgent need to design and develop laser protection materials that can provide "high power densities and long protective duration". Currently, laser protection materials primarily offer a single mode of protection. The main types include reflective, ablative and thermal insulating materials. Ablative materials possess high ablation enthalpy and dissipate laser energy through thermochemical reactions. However, there will be a significant mass loss altering the aerodynamic shape of equipment, which may lead to functional failures. Thermal insulation materials feature low thermal conductivity, slowing heat transfer towards the substrate. Yet, they are prone to trigger localized heat accumulation, resulting in local damage. High-reflectivity materials dissipate laser energy through reflection, reducing energy accumulation in the substrate. However, among the reported high-reflection materials, metals possess low melting points and film materials have poor temperature resistance. These suffer from low protection thresholds, limiting their application. In recent years, high-entropy oxide (HEOs) ceramics have emerged as a research hotspot. Compared with traditional materials, entropy induced the lattice distortion enhances intrinsic phonon scattering, reducing the mean free path, which lowers lattice thermal conductivity. This property maximizes the delay in heat transfer to the substrate, protecting it from damage. Furthermore, high dielectric constants further dissipate laser energy, minimizing energy deposition. Moreover, HEOs exhibit outstanding physicochemical properties in optical, thermal, electrical, magnetic and mechanical fields. Therefore, HEOs hold promise for simultaneously blocking and dissipating laser energy, offering a new material choice for laser protection in critical equipment. Herein, we review the current status and challenges of high-energy laser protection materials in recent years. The high-entropy effects, preparation methods and material systems of HEOs are discussed in detail And the evolution patterns of main properties in laser protection are summarized, including thermal and optical properties. Future research directions are also outlined, along with recommendations for important focus areas.[Progress] Firstly, the four core high-entropy effects of HEOs are introduced, including thermodynamic high-entropy effect, crystallographic lattice distortion effect, kinetic sluggish diffusion effect and "cocktail" effect in performance. The significant role of these effects in phase formation and stabilization is discussed. Secondly, the preparation techniques for HEOs are examined, comparing differences in morphology, structure, purity and reactivity between the wet chemical methods and the solid-state synthesis, along with their respective advantages and disadvantages. Subsequently, the reported typical HEOs are introduced. Driven by entropy engineering, HEOs offer a richer compositional design sequence. The tunability of multiple cations provide new pathways for discovering new structures and properties. Bandgap engineering and phonon engineering further allow for tailoring the diversity of electronic structures, revealing the great application potential of HEOs in laser protection. Finally, the main properties of HEOs in laser protection are discussed. Their low thermal conductivity, anisotropic thermal expansion and high dielectric constants make them promising for new thermoelectric ceramics and ultra-high-temperature structural ceramics in extreme environments. These materials can be developed into laser protection materials with excellent mechanical, thermal, oxidation-resistant, corrosion-resistant, radiation-resistant and high-temperature creep resistance properties for extreme service environments.[Conclusions and prospects] This review is aimed to summarize latest research progress in the application of HEOs in the field of laser protection. Through the synthesis design and functional optimization of HEOs, high-performance laser protection materials can be developed, accelerating their practical application. However, current research faces challenges. Limited understanding of the synergistic mechanism between the multi-effect interactions hinders precise performance tuning to meet current demands, requiring further exploration. The rich compositional design makes manual screening of optimal materials difficult from the large number of element combinations. With advancements in machine learning algorithms, neural networks and AI, data-driven prediction of tailored HEOs shows great potential.

Key words: laser protection; high-entropy oxides; ceramics