Perovskites formation

Gas composition Decomposition on heating AC Perovskite formation on heatingAC Decomposition on cooUngAC Equilibrium 3-phase field rangeAC... 

Composition Decomposition on heating/OsJ mol ) Perovskite formation on heating/QnJ moF )... 

It can be found that most of the systems without 1 1 compound formation have the radius ratio (Rj/Rx) 0.414. This fact can be explained by Pauling s first rule about the structure of complex ionic crystalline compounds (Rb/Rx) 0.414 means the BXg octahedron unstable, while BXe octahedron is one of the basic parts of perovskite structure. Therefore compounds ABX3 with (Ri/Rx) 0.414 can not form stable perovskite-type lattice, even if the value of tolerance factor t is in the favorable range for perovskite formation. 

Heavily exposed X-ray patterns of the fired specimens showed both hematite, a-Fe203, and the perovskite GdFe03 to be present in small amounts in both high and low temperature samples. Holmquist et al. and Rubin-chick et al. ( ) also observed perovskite formation in the reaction between 3Y2O3 and 5Fe203 in the same temperature region. The present perovskite... 

Kakihana et al. [43] and Popa et al. [44] observed a complete ciystallization of LaMnOs prepared by Pechini method at 700°C, with a monophase perovskite formation after calcination at 900°C. On the other hand, a lot of other phases (SrO, La20s and Mn304) were observed by Yang et al. [28] for LSM synthesized with CA MI ratio of 4 and calcined at 900°C. 

Schneider and Roth (1960), using ionic radii given by Ahrens (1952), have suggested from their observations that a minimum radius difference of 0.25 A is necessary for a stable perovskite phase to form. Furthermore, using the tolerance factor derived by Goldschmidt et al. (1926) for this structure type, they proposed again a minimum value of 0.77-0.79 for perovskite formation in these interlanthanide systems. As the tolerance factor tends to unity, so the tendency for stable perovskite formation increases. 

LaFei.xCOxOs (x = 0 or 0.4) perovskites were obtained by nanocasting using Fluka 05120 and Black Pearls 2000 conunercial carbons, which act as hard template during the gel formation and subsequently limiting the particle growing during the perovskite formation. Perovskites with the same nominal composition were also conventionally prepared. The results clearly showed that both commercial carbons was efficient to prepare perovskites with nanosized nature and specific surface area substantially improved. In addition, catalytic tests in the reduction of NO with CO evidenced the better activity of the nanocast perovskites. 

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