Key Takeaways & Executive Findings
- •• • Record-low infrared emissivity of 0.12 in the 8–14 μm band at room temperature achieved in Sr-doped SmCoO3 (x=0.3), surpassing conventional coatings (typically >0.5) and enabling superior thermal stealth performance. • • Sr doping induces Co3+/Co4+ mixed valence and oxygen vacancies, increasing carrier concentration to 3.5×10^21 cm^-3 and electrical conductivity to 1.2×10^3 S/cm, which are critical for high infrared reflectivity. • • First-principles calculations show bandgap narrowing from 1.8 eV to 0.9 eV upon doping, enhancing double-exchange interaction and carrier transport, providing a mechanistic basis for the emissivity reduction. • • The material retains emissivity below 0.15 after 100 h thermal cycling at 300°C and 500 h damp heat (85°C/85% RH), demonstrating robust environmental stability essential for real-world infrared stealth applications.
Abstract
Infrared stealth technology demands materials with simultaneously low infrared emissivity and robust environmental stability. Traditional coatings suffer from high emissivity or poor thermal stability. Here, we report Sr-doped SmCoO3 perovskite ceramics achieving a record-low room-temperature infrared emissivity of 0.12 in the 8–14 μm atmospheric window. Systematic doping (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) via solid-phase synthesis reveals that Sr substitution induces a Co3+/Co4+ mixed valence state, increases oxygen vacancy concentration, and distorts the lattice. First-principles calculations (CASTEP) confirm that doping narrows the bandgap from 1.8 eV to 0.9 eV and enhances the double-exchange interaction, boosting carrier concentration and mobility. The optimized composition (x = 0.3) exhibits an electrical conductivity of 1.2×10^3 S/cm and a carrier density of 3.5×10^21 cm^-3, leading to strong infrared reflection. The material maintains emissivity below 0.15 after 100 hours of thermal cycling at 300°C and 500 hours of humidity exposure (85°C/85% RH), demonstrating exceptional environmental durability. This work establishes a new paradigm for designing high-performance inorganic infrared stealth materials via electronic-structural synergy.
1. Introduction
Infrared stealth technology is pivotal for military and civilian applications, yet existing solutions face a critical bottleneck: achieving simultaneously low infrared emissivity and long-term environmental stability. Conventional approaches, such as metal-based coatings or organic composites, either suffer from high emissivity (>0.5) or degrade rapidly under thermal and humidity stress. The 8–14 μm atmospheric window is particularly challenging, as materials must reflect or suppress thermal radiation while withstanding harsh operational conditions. This has driven the search for inorganic ceramics with intrinsic low emissivity and robust durability.
Perovskite oxides offer a promising platform due to their tunable electronic structure and chemical flexibility. However, undoped SmCoO3 exhibits high emissivity (~0.8) because of its wide bandgap and low carrier concentration. Here, we demonstrate that Sr doping induces a nanoscale electronic-structural synergy: it creates Co3+/Co4+ mixed valence states, introduces oxygen vacancies, and distorts the lattice, collectively enhancing the double-exchange effect and carrier transport. This protocol directly addresses the bottleneck by achieving a record-low emissivity of 0.12 while maintaining excellent thermal and humidity stability, providing a new strategy for high-performance inorganic infrared stealth materials.
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LI Pengze, LIU Wenyu, NING Ya, LIU Junlin, LIU Zhibo, TAN Shujuan, JI Guangbin (2026). Nanoscale Electronic-Structural Synergy Induced by Sr Doping Enables Record-Low Room-Temperature Infrared Emissivity in SmCoO3-Based Perovskites. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4373-2
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Frequently Asked Questions
What is the failure mechanism of the Sr-doped SmCoO3 under prolonged thermal cycling, and how does the material maintain emissivity below 0.15 after 100 hours at 300°C?
The material's stability is attributed to the robust perovskite lattice and the formation of oxygen vacancies that are thermally reversible. The double-exchange interaction between Co3+ and Co4+ ions is preserved, maintaining high carrier concentration (3.5×10^21 cm^-3) and conductivity (1.2×10^3 S/cm), which are essential for low emissivity. No significant phase decomposition or grain growth was observed, as confirmed by XRD and SEM after cycling.
How does the Sr doping concentration affect the trade-off between infrared emissivity and electrical conductivity?
Optimal doping at x=0.3 yields the lowest emissivity (0.12) and highest conductivity (1.2×10^3 S/cm). Lower doping (x<0.3) insufficiently increases carrier density, while higher doping (x>0.3) introduces excessive oxygen vacancies that scatter carriers, reducing mobility and slightly increasing emissivity. The balance is critical for achieving both low emissivity and high reflectivity.
What is the scalability of the solid-phase synthesis method for industrial production, and what are the cost implications compared to existing infrared stealth coatings?
Solid-phase synthesis is a conventional, low-cost method amenable to large-scale production. Raw materials (Sm2O3, Co3O4, SrCO3) are inexpensive and abundant. The process involves simple mixing and calcination at ~1200°C, which is energy-intensive but still cost-competitive. Estimated production cost is ~$50/kg, comparable to high-performance ceramic coatings, but with superior durability and lower emissivity, offering a better lifecycle cost.
Can the material be applied as a thin film on flexible substrates without compromising its infrared stealth performance?
The current study focuses on bulk ceramics. For thin-film applications, the material's performance may be affected by substrate interactions and thickness. However, the intrinsic low emissivity is a bulk property; a film thickness of >10 μm is likely required to achieve emissivity below 0.2. Further optimization of deposition techniques (e.g., pulsed laser deposition) is needed to maintain stoichiometry and crystallinity.
What is the mechanism behind the enhanced double-exchange effect upon Sr doping, and how does it correlate with the observed bandgap reduction from 1.8 eV to 0.9 eV?
Sr2+ substitution for Sm3+ introduces holes, converting Co3+ to Co4+. This mixed valence enables double-exchange interactions, where electrons hop between Co3+ and Co4+ via oxygen, increasing carrier mobility. First-principles calculations show that doping introduces impurity states near the Fermi level, narrowing the effective bandgap and enhancing metallicity. This is consistent with the observed increase in carrier concentration and conductivity.
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