Complex perovskite-type oxide

The pure compounds are divided into simple perovskite-type oxides and complex perovskite-t)fpe oxides. Simple perovskite-type oxides have the chemical formula A +B +03 or A +B" +03. Complex perovskite-type oxides have chemical formulas expressed by (A +Af+)B03, A2+(B2+Bf+)03,... 

A2+(bM+)03, a2+(B2+B 5+p A2+(B2+Bf+)03, A(B, B, B 003, or (A, A0(B, BOO3. Among the complex perovskite-type oxides, most of the Pb(B, BOO3-type oxides show a diffuse phase transition such that the transition point is smeared out over a relatively wide temperature range and exhibits a characteristic dielectric relaxation these materials therefore are called relaxors . 

Many ternary oxides with compositions of A B O3, A B O3, A B O3, A +B + 03, and an abundance of compounds with more complex compositions, are crystallized in perovskite structure. The perovskite structure is very flexible, allowing not only the substitution of different cations in positions A and B over a wide range of compositions Ai xA xBi xBx03, but also the introduction of vacancies or substitutions on the anion sublattice. It is for this reason that about 90% of the metallic elements of the Periodic Table are known to be stable in a perovskite-type oxide structure. 

This method is useful in the preparation of perovskite type oxides and other complex oxides as they allow to obtain pure phase products and to control their stoichiometry. Neodymium aluminates NdAlOs and gadolinium strontium aluminates Gdi.xSrxA103 were synthesized [26, 27, 34-36]... 

In order to examine the mechanism of the oxygen reduction in Lai xSrx. Coi yFey03 5 (LSCF) in this paper, complex studies over the stracture of the ionic and electronic defects, resulting from the deviation from stoichiometry or doping with different ions, were carried as a function of temperature and oxygen partial pressure. The results allowed for designing functional properties of perovskite-type oxides, perspective cathode materials for electrochemically effective IT-SOFC. 

Bismuth oxide forms a number of complex mixed-metal phases with the divalent metal oxides of calcium, strontium, barium, lead, and cadmium, and these show a wide variety in composition. With transition metal oxides, mixed-metal oxide phases have been observed which are based upon a Perovskite-type lattice (10) containing layers of Bi202. It is notable that the high Tc superconducting materials which include bismuth also have this Perovskite-type of lattice with layers of copper oxide interleaved with bismuth oxide layers. 

The pyroelectric response of ferroelectrics may be exploited to detect tem-peratnre changes with extremely high sensitivity. The most common devices are nncooled infrared (IR) detectors, which may be used for spectroscopic analysis as well as imaging apphcations. Pyroelectric thin films based on perovskite-type complex oxides, including Pb(Sc,Ta)03 have been deposited by CSD for intruder alarms, gas sensors, and IR cameras. It is anticipated that these thin-film devices will be substantially less expensive to manufacture than existing bulk polycrystaUine devices, which require labor-intensive manufacturing procedures. 

The reaction between the active compound and the washcoat can be avoided following two approaches. The first approach is to stabilize the active phase by applying it as a complex oxide. The spinel-type oxides, mentioned above, are relatively inactive. On the other hand, perovksites, often AMO3 (A = rare earth metal, e.g.. La, Sr M — transition metal, e.g., Co, Cr, Fe), exhibit promising behavior, which has attracted much attention [55,90,91]. Perovskites may also be used as unsupported oxides, but their surface area is small and not particularly thermostable. The activity of perovskites is dependent mostly on the M cation, but the A cation also has a significant effect [91]. Partial substitution... 

The perovskite-type catalysts (ref.l), other non noble metal complex oxides catalysts (ref.2), and mixed metal oxides catalysts (ref.3) have been studied in our laboratory. The various preparation techniques of catalysts (ref.4 and 5), the adsorption and thermal desorption of CO, C2H5 and O2 (ref.6 and 7), the reactivity of lattice oxygen (ref.8), the electric conductance of catalysts (ref.9), the pattern of poisoning by SO2 (ref. 10 and 11), the improvement of crushing strength of support (ref. 12) and determination of the activated surface of complex metal oxides (ref. 13) have also been reported. 

Extension of the microemulsion reaction method to complex oxides has been explored for a wide variety of materials, including aluminosilicate zeolite [45,108] ferrites [109], mullite [110], barium titanate [111,112], and various perovskite-type mixed oxides [112,113], yttrium-iron garnets (YIGs) [114,115], and high TV superconducting oxides [116-120]. 

Calcination of the oxalate coprecipitates readily yielded phase-pure perovskite-type complex metal oxides. The required calcinations for the microemulsion-derived mixed oxalates were 100-250"C below the temperatures used for oxalates prepared in homogeneous aqueous solutions. 

The most numerous compounds with the perovskite stmcture are complex oxides, although some halides, nitrides, carbides and hydrides may also crystallize in this stmcture. In general, the complex compounds with perovskite-type stmcture are today referred to as perovskites. ... 

Study on the preparation of nanometer perovskite-type complex oxide LaFeOj by sol-gel method ... 

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