posted on 2024-02-26, 15:06authored byXin Zhang, Yiwen Wang, Orest M. Ivasishin, Jiaqi Zhang, Long Yuan
Inorganic
thermochromic materials exhibit a tunable color gamut
and a wide chromatic temperature range, indicating their potential
for intelligent adaptive applications in thermal warning, temperature
indication, thermal regulation, and interactive light-to-thermal energy
conversion. However, most metal-oxide-based thermochromic materials
show weak chromaticity adaption with the change of temperature, which
needs further understanding of the microscopic principle to clarify
the potential route to improve the contrast and identifiability for
fabricating better thermochromic materials. Using perovskite-structure
(AMO3) alkaline earth metal stannate (Ba1–xSrxSnO3, 0.0
≤ x ≤ 1.0) as a model system, this
paper reports for the first time the mechanism of the properties of
thermally induced defect-enhanced charge transfer-type (CTT) thermochromic
materials and the strategy for regulating their thermochromic properties
by A-site cations. BaSnO3 exhibits continuously reversible
thermochromic properties with high contrast from weak light yellow
(b* = 11) to strong bright yellow (b* = 58) between room temperature and 550 °C. In-situ high-temperature
X-ray diffraction (in-situ XRD), in-situ UV–vis absorption
spectroscopy (in-situ UV–vis), thermogravimetric (TG), and
electron paramagnetic resonance (EPR) spectra indicate that this excellent
thermochromic phenomenon is attributed to the weakening of Sn–O
bond hybridization at high temperatures, as well as the formation
of a large number of oxygen vacancies at the top of the valence band,
and the enhanced charge transfer resulting from the generation of
impurity levels in the Sn2+ 5s2 intermediate.
Replacing Ba2+ by Sr2+ in Ba1–xSrxSnO3 successfully
tuned the thermochromic properties, which is attributed to the Sr2+ doping level-directed oxygen defect concentration and deoxygenation
rate. The demonstrated defect-enhanced charge transfer behavior promotes
a feasible route for lattice oxygen-mediated thermochromic materials
and provides a fundamental relationship between thermally induced
defects and colorimetry.