Harnessing the topotactic transition in oxide heterostructures for fast and high-efficiency electrochromic applications

Abstract

Mobile oxygen vacancies offer a substantial potential to broaden the range of optical functionalities of complex transition metal oxides due to their high mobility and the interplay with correlated electrons. Here, we report a large electro-absorptive optical variation induced by a topotactic transition via oxygen vacancy fluidic motion in calcium ferrite with large-scale uniformity. The coloration efficiency reaches ~80 cm2 C−1, which means that a 300-nm-thick layer blocks 99% of transmitted visible light by the electrical switching. By tracking the color propagation, oxygen vacancy mobility can be estimated to be 10−8 cm2 s−1 V−1 near 300°C, which is a giant value attained due to the mosaic pseudomonoclinic film stabilized on LaAlO3 substrate. First-principles calculations reveal that the defect density modulation associated with hole charge injection causes a prominent change in electron correlation, resulting in the light absorption modulation. Our findings will pave the pathway for practical topotactic electrochromic applications.

Control of Oxygen Vacancy Ordering in Brownmillerite Thin Films via Ionic Liquid Gating

“…The oxygen vacancies can give rise to phase transitions, for example, between metallic and insulating states, and can significantly modify the electrical, magnetic, and optical properties. − The oxygen vacancies also influence ionic transport that is key to the operation of devices for resistive switching and catalysis. − In many cases, the oxygen vacancies form ordered arrays. An important example are the brownmillerite ( BM ) phases that are formed from the parent perovskite phase by the removal of oxygen in alternate layers: representative examples are SrCoO 2.5 , ,− BaInO 2.5 , La 1– x Sr x CoO 3‑δ , − SrFeO 2.5 , − SrFe 1– x Co x O 2.5 , and CaFeO 2.5 . − In these phases, oxygen vacancy channels (OVCs) are formed within the oxygen deficient layers. The OVCs can provide paths for fast ionic diffusion or storage of ions, , leading to applications in fuel cells and rechargeable batteries.…”

Time Evolution of the Structural, Electronic, and Magnetic Phases in Relaxed SrCoO3 Thin Films

“…For example, the BM−CaFeO 2.5 thin film on the LaAlO 3 substrate has a granular structure, where the grain boundaries play a role of fast tracks through which oxygen vacancies can migrate more rapidly in the film to reach the P−CaFeO 3 phase via applying an electric field. 31 However, the topographies of both the SrCoO 3 thin films are very smooth, as can be seen from the field emission scanning electron microscopy (FESEM) images taken on the initial day of thin-film preparation (Figure 4d). Therefore, the grain boundaries do not play any role in faster oxygen reduction in the relaxed SrCoO 3 film than in the strained film.…”

“…The different crystalline qualities could be the cause of different oxygen reduction rates between the strained and relaxed SrCoO 3 thin films. For example, the BM–CaFeO 2.5 thin film on the LaAlO 3 substrate has a granular structure, where the grain boundaries play a role of fast tracks through which oxygen vacancies can migrate more rapidly in the film to reach the P–CaFeO 3 phase via applying an electric field . However, the topographies of both the SrCoO 3 thin films are very smooth, as can be seen from the field emission scanning electron microscopy (FESEM) images taken on the initial day of thin-film preparation (Figure d).…”

Enhanced Contrast of WO3-Based Smart Windows by Continuous Li-Ion Insertion and Metal Electroplating

“…Heating, ventilation, air conditioning (HVAC), and lighting in the buildings account for 30–40% of the primary energy consumption in the world. − Therefore, it is compulsory to develop technologies to dynamically alter the optical or thermal properties in the buildings to reduce the energy consumption. Electrochromic smart windows (ESWs) are considered to be an effective way to diminish the energy usage by controlling the optical transmittance properties, which can decrease 20% energy consumption compared to static low-emissivity windows, thus attracting much attention in this area. − …”