Evolution of Perovskite Synthesis

Oxides form the most common and interesting compounds with perovskite structure. Almost all the metallic natural elements in the periodic table are found in stable perovskites. Also, materials with this structure can be obtained by partial substitution of one or more metallic elements in the A site and/or in the B site. The wide range of properties shown by perovskite-type oxides find applications in catalysis, magnetism, solid oxide fuel cells, and superconductivity. Proper combination or partial substitution of the A site and/or B site atoms introduces abnormal valences or lattice defects, which in turn gives rise to interesting changes in their properties. 

Various strategies were developed in the past for the synthesis of perovskite-structured oxides (Table 3.1). Of these, the choice of a particular method depends on the type of application expected. For catalytic applications, specific surfece area and crystal structure play crucial roles. Hence, the synthesis of these materials for catalytic applications always focused on obtaining crystalline materials with high values of specific surface area. The oldest method for the synthesis of perovskite-structured mixed metal oxides is the ceramic method. In this method, thoroughly mixed precursors (oxides, hydroxides, or carbonates) of the metals are calcined at elevated temperatures ( 800 °C) for several hours. The surfece area of thus synthesized perovskites was, however, found to be less than 5m /g [5,30]. The high temperature used in solid-state reactions, for perovskite crystallization, results in the sintering of particles, which in turn leads to a large 

Sbet is the specific surface area determined by the BET method. 

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