This study proposes a strategy based on heterovalent ion doping that gives rise to a synergistic piezo-phototronic effect with significantly improved catalytic activity and leads to selective catalytic enhancement for specific pollutants. Owing to the enhanced light absorption, hydrogen evolution rates are as high as 3704 and 3178 µmolg −1 h −1 in 0.01Li-doped BaTiO 3 and 0.02La-doped BaTiO 3 nanosheets, respectively, under simultaneous irradiation by ultrasound and light, a factor of 4.6 and 3.9 times higher than for pure BaTiO 3 . The performance also far exceeds that of single piezocatalysis, photocatalysis, or the sum of the two for Li/La-doped BaTiO 3 nanosheets due to the effects of the piezoelectric field in promoting photo-induced separation of electron-hole pairs. Further, by carefully selecting donor or acceptor doping, a significant enhancement in catalyst to specific pollutants is obtained by controlling the band structure. Compared to pure BaTiO 3 , 0.01Li-doped BaTiO 3 possesses higher catalytic activity for anionic dyes such as Methyl blue and Malachite Green, reaching 0.067 and 1.379 min −1 , respectively, while 0.02La-doped BaTiO 3 exhibits better catalytic performance for cationic dyes such as Rhodamine B and Methyl Orange, with degradation rates up to 0.274 and 0.029 min −1 , respectively. This study offers a path to the design of efficient piezocatalysts for specific applications.
In this paper, some nonplanar metagratings with multilevel asymmetric grooves are demonstrated to produce broadband and high‐efficiency anomalous reflection in wide‐incident‐angle range. First, bipartite metagrating with two asymmetric grooves per unit cell is proposed and optimized by machine learning. It can not only realize a high efficiency (≈88.8%) and large‐angle (≈70°) anomalous reflection under normal incidence, but also preserve the high performance over broad bandwidth (12.0–20.0 GHz) and wide‐incident‐angle range. Furthermore, to improve the large‐angle anomalous reflection at low frequencies, a tripartite metagrating is designed. The participation of more cavity modes makes the metagrating achieve the anomalous reflection with an efficiency greater than 90% over a broader bandwidth from ±1st Rayleigh anomalies to 20.0 GHz (even higher) and a wide range of incident angles from −70° to 70°, which is verified by the experimental measurement. Especially at an incident angle of 20°, the high‐efficiency anomalous reflection is sustained over an ultrabroad frequency range from 9.7 to 21.2 GHz, i.e., a fractional bandwidth of 74.4%. The excellent performance of anomalous reflection and relatively simple structures endow the asymmetric groove metagratings with abundant functions, such as ideal three‐channel retroreflector and abnormal reflector, and make them attractive in highly efficient and extreme wave manipulation.
Phase transition plays a key role in the electrocaloric effect, but the first-order ferroelectric-paraelectric phase transition always occurs far above room temperature, which heavily limits the practical application. Herein, the focus is on the orthorhombic-tetragonal first-order ferroelectric-ferroelectric phase transition (@288 K) in <011>-oriented barium titanate single crystal. Ferroelectric properties under a high electric field indicate a reversible field-induced tetragonal-orthorhombic phase transition, based on which the electric fieldtemperature phase diagram is established. It is strongly related to the enhanced electrocaloric effect, and a large adiabatic temperature change of 1.33 K is obtained at 288 K under 15 kV cm À1 , that is, a high electrocaloric strength of 88.7 mK cm kV À1 . The large electrocaloric effect near room temperature makes lead-free BaTiO 3 a promising candidate for next-generation solid-state refrigeration.
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