Excellent performance of AgNbO3 in adaptive photothermal management via ferroelectric-to-paraelectric phase transition

Adaptive photothermal management (APM) materials with large emissivity variation and low solar absorptivity are vital in the field of smart thermal control. However, the related variable emission mechanism in phase-changing progress for adaptively photothermal modulating material suffers from drawbacks of diversity, complexity and uncertainty. Herein, AgNbO 3 (ANO) is discovered as a new promising APM material with low solar absorptivity and large emissivity variation after density functional theory (DFT) calculation and experimental demonstration on five types of phases for ANO. The ANO ceramic is prepared by solid-state reaction method with high temperature, appearing ferrielectric orthorhombic (M1, Pmc2 1 ), antiferroelectric orthorhombic (M2, Pbcm), antiferroelectric orthorhombic (M3, Pbcm), paraelectric orthorhombic (O, Cmcm), and paraelectric tetragonal (T, P4/mbm) phases. Meanwhile, the obtained ANO ceramic has both a low solar absorptivity of 0.1886 in 250–2500 nm, and exhibits a large emissivity variation of 0.4242 in 300–860 K. The comprehensive performance of both low solar absorptivity and large emissivity variation for ANO ceramic is superior to the best available intelligent thermal control materials (low solar absorptivity and large emissivity variation are difficult to coexist in one component). The low solar absorptivity, dielectric permittivity, and phase transition temperature could be attributed to the big crystallite size, while the influence of surface crystallite size on average emissivity could be ignored. Additionally, mechanisms of Nb─O and Ag─O bonds for the emissivity in phase-changing progress are proposed by establishing the relationship between the orbital character of the density of states and the infrared emissivity. Furthermore, the effect of polarization on emissivity is revealed. This work will guide APM materials selection and preparation toward desired emissivity and solar absorptivity to satisfy numerous applications.