A strategy of hierarchical particle-pore scattering in La-Al co-doped CaTiO₃ ceramics for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) has emerged as a promising electricity-free strategy for reducing building energy consumption. Most PDRC research focuses on tailoring optical properties, namely high ultraviolet–visible-near-infrared (UV–vis-NIR) reflectivity and high infrared emissivity (IR_e); however, environmental heat gain remains a critical barrier to achieving stable sub-ambient cooling. Here, we report a La-Al co-doped CaTiO₃ ceramic synthesized via a solid-state reaction combined with 36 h of ball milling and 1200 °C sintering. By prolonging the milling duration and moderating the sintering temperature, the hierarchical particle-pore microstructure with experimentally measured distributions was achieved, leading to enhanced Mie scattering, as confirmed by finite-difference time-domain (FDTD) simulations. As a result, the optimized ceramic material exhibits an ultrahigh average UV–vis-NIR reflectivity of 99% and a high atmospheric transparency window (ATW; 8–14 µm) infrared emissivity (IR_e) of 0.97. In indoor/outdoor simulated solar irradiation of 700–1000 W/m², the ceramic achieved a maximum temperature reduction of 7.7 °C with an average reduction of 7.2 and 6.8 °C and an average radiative cooling power of ∼ 103.56 and ∼ 97.53 W/m². Moreover, the ceramic material demonstrates excellent chemical durability, maintaining stable performance under weather chamber and salt spray environments. This work presents a scalable, cost-effective route to high-performance PDRC ceramics, offering a robust solution for long-term, energy-efficient building-cooling applications.