Engineering the optical properties of SrZrO <sub>3</sub> crystals via Zn doping for superior passive daytime radiative cooling
Yangyang Li, Yichuan Yin, Yu Bai, Hongying Dong, Ting Yang, Yuanming Gao, Wen Ma
Abstract
As global energy consumption rises, developing efficient energy - saving materials is crucial for alleviating energy pressure. Passive daytime radiative cooling materials are promising for energy - free refrigeration. SrZrO<sub>3</sub> crystal’s wide band gap and infrared photon lattice vibration absorption make it a potential passive daytime radiative cooling material, but its solar reflectivity and atmospheric window emissivity can be further enhanced. For this purpose, a series of Zn-doped SrZrO<sub>3</sub> crystals were prepared by sol-gel method combined with solid phase synthesis method. The effects of Zn doping on SrZrO<sub>3</sub> crystal’s phase structure, electronic structure, spectral radiative characteristics, and passive daytime radiative cooling performance were investigated by experiments and theoretical calculations. The results show that, on the one hand, the changes of grain morphology and electronic structure caused by Zn doping jointly determine the improvement of the reflection performance of the crystals in the wavelength of 0.3-2.5 μm. On the other hand, the lattice distortion and the decrease of lattice symmetry caused by Zn doping lead to the increase of photon emissivity for 8-13 μm band. The solar reflectivity of SrZr<sub>0.75</sub>Zn<sub>0.25</sub>O<sub>2.75</sub> crystal powder can reach 0.892, whereas the atmospheric window emissivity can reach 0.954, both are higher than that of SrZrO<sub>3</sub>. The coating prepared by SrZr<sub>0.75</sub>Zn<sub>0.25</sub>O<sub>2.75</sub> crystal powder as the radiative refrigerant can reach the maximum radiative cooling temperature of 15.3 ℃ under the solar irradiation of 654 W·m<sup>-2</sup>, and the maximum net radiative power is 64.7 W·m<sup>-2</sup>. These results indicate that SrZr<sub>0.75</sub>Zn<sub>0.25</sub>O<sub>2.75</sub> is an excellent passive daytime radiative cooling material.