In response to the development concept of “carbon neutrality” and “carbon peak”, it is critical to develop materials with high near-infrared (NIR) solar reflectivity and high emissivity in atmospheric transparency window (ATW, 8-13 μm) to advance zero energy consumption radiative cooling technology. To achieve the regulation of emission and reflection properties, a series of high-entropy rare earth stannate ceramics (HE-RE₂Sn₂O₇: (Y_0.2La_0.2Nd_0.2Eu_0.2Gd_0.2)₂Sn₂O₇, (Y_0.2La_0.2Sm_0.2Eu_0.2Lu_0.2)₂Sn₂O₇, (Y_0.2La_0.2Gd_0.2Yb_0.2Lu_0.2)₂Sn₂O₇) with seriously lattice distortion were prepared using the solid phase reaction followed by pressureless sintering method for the first time. The lattice distortion is accomplished by introducing rare earth elements with different cation radius and masses. The as-synthesized HE-RE₂Sn₂O₇ ceramics possess high ATW emissivity (91.38%~95.41%), high NIR solar reflectivity (92.74%~97.62%), low thermal conductivity (1.080~1.619 W·m^-1·K^-1) and excellent chemistry stability. On the one hand, the lattice distortion intensifies the asymmetry of the structural unit to cause a notable alteration in the electric dipole moment, ultimately enlarging the ATW emissivity. On the other hand, through selecting excitation-difficult elements, HE-RE₂Sn₂O₇ with a wide band gap exhibits high NIR solar reflectivity. Hence, the multi-component design can effectively enhance the radiative cooling ability of HE-RE₂Sn₂O₇ and provide a novel strategy for developing radiative cooling materials.

YSZ has been widely used as a TBC material, but its phase change at high temperatures limits its development, thus the need for developing new thermal barrier materials resistant to high temperatures. Rare-earth aluminate ceramics with a garnet structure (Yb₃Al₅O₁₂) have been considered as a potential thermal barrier material. The melting point of Yb₃Al₅O₁₂ is 2000 °C, which has a potential high temperature application prospect. However, Yb₃Al₅O₁₂ has lower thermal expansion and higher thermal conductivity than YSZ, which is a widely employed thermal barrier coating (TBC) material. To overcome these obstacles, (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂, a high-entropy ceramic, was prepared by a solid-state reaction and pressureless sintering. The thermal conductivity of the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ was 3.48 W/(m·K) at 300 K, approximately 25.48% lower than that of the Yb3Al5O12 (4.67 W/(m·K)). The thermal expansion coefficient of the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ was 9.28 × 10⁻⁶ K⁻¹ at 673-1273 K, approximately 18.52% higher than that of the Yb₃Al₅O₁₂ (7.83 × 10⁻⁶ K⁻¹, 673-1273 K). When the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ was annealed at 1550 °C for 7 days, its average grain size only increased from 0.7 μm to 1.3 μm. Moreover, the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ exhibited better chemical stability and a lower grain growth rate than the Yb₃Al₅O₁₂. This study reveals that (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ is a promising candidate for the future generation of thermal barrier materials.

Betavoltaic batteries, as a kind of ultimate battery, have attracted much attention. ZnO is a promising wide-bandgap semiconductor material that has great potential in solar cells, photodetectors, and photocatalysis. In this study, rare-earth (Ce, Sm, and Y)-doped ZnO nanofibers were synthesized using advanced electrospinning technology. The structure and properties of the synthesized materials were tested and analyzed. As betavoltaic battery energy conversion materials, the results show that rare-earth doping increases the UV absorbance and the specific surface area and slightly reduces the band gap. In terms of electrical performance, a deep UV (254 nm) and X-ray source (10 keV) were used to simulate a radioisotope β-source to evaluate the basic electrical properties. Among them, the output current density of Y-doped ZnO nanofibers can reach 87 nA·cm–2, which is 78% higher than that of traditional ZnO nanofibers, by deep UV. Besides, the photocurrent response of Y-doped ZnO nanofibers is superior to that of Ce-doped and Sm-doped ZnO nanofibers by soft X-ray. This study provides a basis for rare-earth-doped ZnO nanofibers as energy conversion devices used in betavoltaic isotope batteries.

Selective emitters are crucial as the key component determining the energy conversion efficiency of Radioisotope Thermophotovoltaic (RTPV) systems. Developing selective emitter materials with high selective emissivity, high spectral efficiency and excellent high-temperature stability can effectively improve the energy conversion efficiency and service life of RTPV systems. In order to adjust the selective emissivity and spectral efficiency, a series of rare earth tantalate selective emitters (Er(Ta_1-xNb_x)O₄ (0≤x≤0.2)) matching GaSb battery were prepared by high-temperature solid-state reaction and pressureless sintering method. The as-prepared Er(Ta_1-xNb_x)O₄ (0≤x≤0.2) ceramics exhibit high emissivity (49%-93%) in the selective band (1.40-1.60 μm), high spectral efficiency (59.46%-62.12%) and excellent high-temperature stability at 1400 ℃. On the one hand, doping Nb⁵⁺ into the B-site changes the crystal local structure symmetry around Er³⁺, which promotes the f-f transition of Er³⁺ and enhances the selective emission performance. On the other hand, doping Nb⁵⁺ ions into the B-site can alter the band gap and oxygen vacancy concentration to suppress non-selective emissivity. Increasing the selective emissivity and reducing the non-selective emissivity is beneficial for improving the spectral efficiency of selective emitters. Hence, the selective emissivity and spectral efficiency of Er(Ta_1-xNb_x)O₄ (0≤x≤0.2) can be effectively enhanced through compositional design, providing a new strategy for developing selective emitter materials for RTPV applications.

The development of a new generation of solid particle solar receivers (SPSRs) with high solar absorptivity (0.28–2.5 μm) and high infrared emissivity (1–22 μm) is crucial and has attracted much attention for the attainment of the goals of “peak carbon” and “carbon neutrality”. To achieve the modulation of infrared emission and solar absorptivity, two types of medium- and high-entropy rare-earth hexaboride (ME/HEREB₆) ceramics, (La_0.25Sm_0.25Ce_0.25Eu_0.25)B₆ (MEREB₆) and (La_0.2Sm_0.2Ce_0.2Eu_0.2Ba_0.2)B₆ (HEREB₆), with severe lattice distortions were synthesized using a high-temperature solid-phase method. Compared to single-phase lanthanum hexaboride (LaB₆), HEREB₆ ceramics show an increase in solar absorptivity from 54.06% to 87.75% in the range of 0.28–2.5 μm and an increase in infrared emissivity from 76.19% to 89.96% in the 1–22 μm wavelength range. On the one hand, decreasing the free electron concentration and the plasma frequency reduces the reflection and ultimately increases the solar absorptivity. On the other hand, the lattice distortion induces changes in the B–B bond length, leading to significant changes in the Raman scattering spectrum, which affects the damping constant and ultimately increases the infrared emissivity. In conclusion, the multicomponent design can effectively improve the solar energy absorption and heat transfer capacity of ME/HEREB₆, thus providing a new avenue for the development of solid particles.

As the flight speed of hypersonic vehicles increases, the airframe temperature rises sharply, which puts forward greater demands for ultra-high temperature thermal protection materials with high infrared emissivity and low thermal conductivity. In this work, LaB₆, (La_1/3Eu_1/3Ca_1/3)B₆ (MEB₆), and (La_1/5Eu_1/5Ca_1/5Ba_1/5Sr_1/5)B₆ (HEB₆) were prepared by boron-carbon thermal reduction and spark plasma sintering. To regulate the thermal conductivity and infrared emissivity, alkaline earth metal elements are introduced into the design of multi-component hexaborides. Among them, the infrared emissivity of HEB₆ in the 1.28-5 μm wavelength range increased from 81.487% to 95.662% compared to LaB₆. Compared with LaB₆, the thermal conductivity of HEB₆ is reduced significantly from 57.640 W·m^-1·K^-1 to 17.041 W·m^-1·K^-1. Among all samples, HEB₆ exhibited the lowest electrical conductivity of 2952.667 S·cm^-1, which was much lower than that of LaB₆ (75826.000 S·cm^-1). This strategy improves the infrared emissivity and reduces thermal conductivity. On the one hand, the introduction of alkaline earth metals reduces the electron density of the material and modulates the electronic band structure, thereby reducing the conductivity and increasing the infrared emissivity. On the other hand, large atomic mass and size differences aggravate the asymmetry of crystal structural units, resulting in enhanced phonon scattering and reduced thermal conductivity. Hence, the increase of emissivity and the decrease of thermal conductivity are simultaneously regulated, providing a new strategy for the development of thermal protection materials for hypersonic vehicles.