Passive radiative cooling (PRC) is a promising way to alleviate the global energy crisis by reflecting sunlight and dissipating heat through the atmospheric transparent window (ATW). Despite possessing a wide bandgap and complex phonon modes, the PRC performance of Mg₂Al₄Si₅O₁₈ is limited by phonon-polariton resonance. Herein, phonon engineering is integrated with bandgap engineering to design and synthesize a series of Mg₂Al₄Si₅O₁₈:xY³⁺ (x = 0%, 2.5%, 5%, 7.5%, and 10%) ceramics with excellent PRC performance. Density functional theory (DFT) identifies that Y³⁺ doping effectively suppresses phonon-polariton resonance and widens the bandgap, synergistically enhancing the PRC performance. The as-prepared samples exhibit high ATW emissivity (94.39%–98.39%) and high reflectivity (89.52%–94.77%) in the 0.4–2.5 μm range. Furthermore, the “cooling glass” coating successfully achieves a maximum temperature reduction of 16.5 °C and an average net radiative cooling power of 113.1 W·m⁻². Y³⁺ doping enhances ATW emissivity by inducing lattice distortion, which reduces symmetry and alters the dipole moment while boosting reflectivity in the visible and near-infrared (vis-NIR) regions by preserving the wide bandgap through the introduction of optically inert elements. This work synergistically integrates the advantages of high performance, low cost, and environmental friendliness, offering a highly promising ceramic material solution for large-scale radiative cooling applications.

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.

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. 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 batteries 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 °C. On 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 bandgap 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.

In response to the development of the concepts of “carbon neutrality” and “carbon peak”, it is critical to developing materials with high near-infrared (NIR) solar reflectivity and high emissivity in the atmospheric transparency window (ATW; 8–13 μm) to advance zero energy consumption radiative cooling technology. To regulate 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, and (Y_0.2La_0.2Gd_0.2Yb_0.2Lu_0.2)₂Sn₂O₇) with severe lattice distortion were prepared using a solid phase reaction followed by a pressureless sintering method for the first time. Lattice distortion is accomplished by introducing rare earth elements with different cation radii and mass. 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 chemical 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, by selecting difficult excitation elements, HE-RE₂Sn₂O₇, which has a wide band gap (E_g), exhibits high NIR solar reflectivity. Hence, the multi-component design can effectively enhance radiative cooling ability of HE-RE₂Sn₂O₇ and provide a novel strategy for developing radiative cooling materials.