Perovskites morphology

Entry (Reference) Perovskite (acronym) Synthesis method coupled with microwaves (MW) Microwave source Reaction conditions (reaction time and temperature under micro-wave irradiation) Remarks/perovskite morphology... 

Entry Perovskite Synthesis Microwave source Reaction conditions (reaction time Remarks/perovskite morphology... 

The work that will be presented in this chapter has been divided into broad categories, according to the perovskite morphology and thus to the type of reactor ... 

In both cases, the replacement product is usually reported as having a distinctly fibrous or prismatic morphology. The higher level of radiation damage in metaloparite (lucasite ) could be due to a difference in the critical amorphization dose of loparite and the alteration product, provided that the alteration event occurred soon after crystallization of the loparite. For example, Smith et al. (1998) and Lumpkin et al. (1998) have shown that the critical amorphization dose of perovskite structure types may be as much as a factor of five greater than the critical dose of other Nb-Ta-Ti minerals (e.g., pyrochlore and zirconolite). 

In this review, the relationships between structure, morphology, and surface reactivity of microcrystals of oxides and halides are assessed. The investigated systems we discuss include alkali halides, alkaline earth oxides, NiO, CoO, NiO-MgO, CoO-MgO solid solutions, ZnO, spinels, cuprous oxide, chromia, ferric oxide, alumina, lanthana, perovskites, anatase, rutile, and chromia/silica. A combination of high-resolution transmission electron microscopy with vibrational spectroscopy of adsorbed probes and of reaction intermediates and calorimetric methods was used to characterize the surface properties. A few examples of reactions catalyzed by oxides are also reported. 2001... 

Regarding the morphology, a polyhedron terminated by the (001) face is expected for cubic II-IV perovskites, i.e., AB03 perovskites in which A and B are divalent and tetravalent, respectively. In these perovskites, two nonpolar (001) surface terminations are possible (AO and BO2). On an A-O terminated surface, the cation A is octa-coordinated, whereas on the BO2 terminated surface the cation B is penta-coordinated. Ill—III perovskites, bulk structures with lower symmetry, are more stable (orthorombic or rhombohe-dral) than II-IV perovskites, and the nonpolar low-index faces are more complex and show a different coordinative environment for both A and B cations. 

Inclusions that are predominantly melilite with minor spinel, perovskite, and hibonite are referred to as Type A. Most Type-A CAIs have a porous structure and are called fluffy Type-A CAIs. Some Type-A CAIs have a compact form and generally rounded shapes. These are referred to as compact Type-A CAIs. Type-B1 CAIs are characterized by coarse-grained, melilite-rich mantles surrounding cores composed of melilite, spinel, fassaite, and anorthite. Type-B2 inclusions have the same mineralogy, but lack the melilite-rich mantle. Type-B3 inclusions contain significant amounts of forsterite in addition to melilite. Type-C inclusions are similar to Type B2s, but anorthite is more abundant than melilite. All Type-B and Type-C inclusions have compact morphologies. 

In contrast to the processes described above, the electrooxidation of metals and alloys still cannot be considered as an accepted electrosynthetic method as yet only its principal possibilities have been demonstrated. At the same time, the anodic oxidation of transition metals, which forms the basis for a number of semiconductor technologies, is extremely effective and convenient for varying and controlling the thickness, morphology, and stoichiometry of oxide films [233]. It therefore cannot be mled out that, as the concepts concerning the anodic behavior of metal components of HTSCs in various media are developed, new approaches will be found. The development of combined methods that include anodic oxidation can also be expected, by analogy with hydrothermal-electrochemical methods used for obtaining perovskites based on titanium [234,235], even at room temperature [236]. 

Solid-solid reactions are the basis of the most frequently used procedures for preparing mixed oxides, especially when the surface areas of the resulting solids are not an important parameter. Indeed, these high-temperature methods are essential for preparing perovskites with special morphologies, such as monocrystals or thin layers. Because this kind of method is most frequently used for the preparation of ceramic materials, it is usually referred to as the ceramic method. ... 

Perovskite-structured membranes, in the form of thin films supported on porous ceramic or metal substrates, have been studied extensively in the past decade. Thin films offer several advantages including reduced material cost, improved mechanical strength and possibly higher H2 flux. Chemical vapor deposition (CVD) [99], electrochemical vapor deposition (EVD) [100] and sputtering [101] represent typical methods. However, dense films have been difficult to obtain by these methods. It was found that the continuity and gas-tightness of the deposited films were very sensitive to the morphologies and pore size of substrates. 

Figure 18.5 Effect of the surface modification by 98% sulfuric acid for 40 min on the LSCF perovskite hollow fiber membranes. (A) Fiber wall after modification (B) surface before modification (Q surface morphology after modification.

The concentration of Ba(OH)2 significantly affects the final morphology of barium titanate nanopowder. The BaTiOs particles acquire spherical shape at sufficiently high concentrations of Ba (OH)2 only. In the opposite case crystals take various anisotropic shapes. Addition of surfactants [90, 94, 100] improves the crystallization of perovskite phase. 

Tan, X., Liu, N., Mengand, B. and Liu, S. (2011) Morphology control of the perovskite hollow fibre membranes for oxygen separation using different bore fluids. Journal of Membrane Science, 378, 308-318. 

Lappas, A. Zorko, A. Wortham, E. Das, R. N. Giannelis, E. P. Cevc, P. Arcon, D., Clay-Low-Energy Magnetic Excitations and Morphology in Layered Hybrid Perovskite-Poly(dimethylsiloxane) Nanocomposites. Chem. Mater. 2005,17, 1199-1207. 

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