34 However, it was still unclear if the PA method can be applied to synthesize versatile perovskites. 31 Recently, we reported the synthesis of LaCoO 3 by the PA method and clarified that the impurities contained in the carbon sources negatively affect the formation of LaCoO 3. Using nanocarbons as the carbon source, the PA method has enabled the synthesis of monoxide nanotubes (SiO 2, Al 2O 3, ZrO 2, NiO, Fe 2O 3) 29,30 and perovskites (LaMnO 3). Subsequently, the calcination process removes the nanocarbon, yielding nanostructured oxides that emulate the nanocarbon morphology. 29–34 Typically, a metal precursor solution is dropped onto the nanocarbon powder, followed by solvent evaporation, which leaves the precursor on the surface of the nanocarbon. Our research group has developed a new strategy, the precursor accumulation (PA) method, to synthesize nanostructured oxides ( Scheme 1).
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Recently, other novel processes to synthesize nano-perovskites have also been reported, such as solid-state gelation and molten-salt-protected pyrolysis. In addition to the sol–gel method, other solution-based approaches, such as coprecipitation, 10,14,15 combustion, 16–18 flame-spray, 19–22 and microemulsion methods, 23,24 have been explored. The low-temperature calcination of the gel yielded nanosized perovskites. 10–13 Typically, a chelating reagent ( e.g., citrate) and a polyol are used to crosslink A- and B-site cations and form a gel with uniformly distributed metal cations. The sol–gel method is a wet process that has been developed based on the aforementioned strategy. The pre-mixing of A- and B-site cations allows the formation of a mixed-oxide structure by low-temperature calcination, as long-distance diffusion of cations into solids is no longer required. Here, a precursor in which different cations are uniformly distributed is beneficial. However, high-temperature calcination must be avoided during the synthesis of nano-perovskites. In the solid-phase method, the diffusion of cations into the crystalline state at high temperatures is the driving force for the formation of perovskites.
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Despite its simplicity, the solid-phase method has disadvantages, such as sintering of perovskite during high-temperature calcination and decreased surface area of perovskite due to the formation of large particles, which are undesirable for some applications such as catalysts. Classical solid-state synthesis is a widely used method in which the precursor (typically a single metal oxide) is physically ground and calcined at high temperatures. To synthesize perovskites, the A- and B-site cations must be uniformly distributed in the oxide structure. 1–9 Chemically, perovskites are oxides with an ABO 3 type structure in which a wide variety of A- and B-site cations can be incorporated thus, they are considered functionally versatile. Introduction Perovskite-type oxides are a class of materials that exhibit unique and superior properties, including dielectric, magnetic, ionic, and electronic transport therefore, they show tremendous potential in various applications such as solar cells, catalysts, sensors, and fuel cells. Various nano-perovskites, including LaMnO 3, LaCoO 3, LaFeO 3, LaNiO 3, LaAlO 3, LaGaO 3, CaMnO 3, BaMnO 3, SrMnO 3, La 0.7Sr 0.3FeO 3, La 2CuO 4, and Ca 2Fe 2O 5, were successfully synthesized, demonstrating the simplicity and novelty of the method for the general synthesis of nano-perovskites. The homogeneity of the precursors facilitated low-temperature calcination that resulted in the formation of nano-perovskites. The accumulation of precursors ( i.e., metal salts) on the surface of the nanocarbon during the evaporation of the solvent is the key step in which the precursors are homogeneously mixed prior to calcination. The calcination of the nanocarbon deposited with metal salts yielded nano-perovskites, emulating the morphology of nanocarbons.
![shimo licent shimo licent](https://img-new.cgtrader.com/items/1871714/534443c547/shimo-rugs-240-3d-model-max-obj-mtl-fbx.jpg)
Herein, various nano-perovskites were synthesized by a facile approach involving the use of nanocarbons. Despite their vast potential in various applications, general and simple synthesis methods for nano-perovskites remain limited. Perovskite-type oxides have impacted various research fields, including materials and energy science.