To minimize this effect new perovskite-type mixed ionic-electronic conducting oxides have been widely studied as promising IT-SOFC cathodes. Among them, iron perovskites LSF seem to be good candidates mainly for their appropriate thermal expansion match with YSZ electrolytes and their good catalytic activity for the oxygen reduction [3,4]. The properties of these compounds and thus their cell performance depends on several factors:
Structure[ edit ] The perovskite structure is adopted by many oxides that have the chemical formula ABO3. The diagram shows edges for an equivalent unit cell with A in the body center position, B at the corners, and O at mid-edge positions.
The relative ion size requirements for stability of the cubic structure are quite stringent, so slight buckling and distortion can produce several lower-symmetry distorted versions, in which the coordination numbers of A cations, B cations or both are reduced.
Tilting of the BO6 octahedra reduces the coordination of an undersized A cation from 12 to as low as 8. Conversely, off-centering of an undersized B cation within its octahedron allows it to attain a stable bonding pattern. The resulting electric dipole is responsible for the property of ferroelectricity and shown by perovskites such as BaTiO3 that distort in this fashion.
The orthorhombic and tetragonal phases are most common non-cubic variants. Complex perovskite structures contain two different B-site cations.
This results in the possibility of ordered and disordered variants. Common occurrence[ edit ] The most common mineral in the Earth is bridgmanite, a magnesium-rich silicate which adopts the perovskite structure at high pressure.
At the pressure and temperature conditions of the lower mantle, the most abundant material is a perovskite-structured mineral with the formula Mg,Fe SiO3, with the second most abundant material likely the rocksalt-structured Mg,Fe O oxide, periclase.
However, it cannot be transported from depths of several hundred km to the Earth's surface without transforming back into less dense materials. At higher pressures, MgSiO3 perovskite transforms to post-perovskite.
Although the most common perovskite compounds contain oxygen, there are a few perovskite compounds that form without oxygen.
Fluoride perovskites such as NaMgF3 are well known. A large family of metallic perovskite compounds can be represented by RT3M R: The metalloids occupy the octahedrally coordinated "B" sites in these compounds.
MgCNi3 is a metallic perovskite compound and has received lot of attention because of its superconducting properties. Materials properties[ edit ] Perovskite materials exhibit many interesting and intriguing properties from both the theoretical and the application point of view.
Colossal magnetoresistanceferroelectricitysuperconductivitycharge orderingspin dependent transport, high thermopower and the interplay of structural, magnetic and transport properties are commonly observed features in this family.
These compounds are used as sensors and catalyst electrodes in certain types of fuel cells  and are candidates for memory devices and spintronics applications. One prime example is yttrium barium copper oxide which can be insulating or superconducting depending on the oxygen content.
Chemical engineers are considering a cobalt-based perovskite material as a replacement for platinum in catalytic converters in diesel vehicles. Because of the flexibility of bond angles inherent in the perovskite structure there are many different types of distortions which can occur from the ideal structure.
These include tilting of the octahedradisplacements of the cations out of the centers of their coordination polyhedra, and distortions of the octahedra driven by electronic factors Jahn-Teller distortions.
It has a high charge carrier mobility and charge carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted as current, instead of losing their energy as heat within the cell.
They also showed that carrier lifetimes in the mixed perovskite are longer than in the pure iodide.Perovskites with two doped sublattices have been studied extensively in recent years with the view of improving characteristics of these materials as proton conductors.
Solubility of hydrogen in these compounds presents an independent interest, because the hydration limit for proton-conducting oxides is often much lower than the concentration. However,taking into account the large variety of metal oxides, the principal objective of thisbook is to examine only metal oxides that are more attractive from the catalyticpoint of view, and most specifically transition metal oxides (TMO).
perovskite oxide has a stoichiometry formula of ABO3 and belongs to the cubic space group Pm3m, with the A cation in a fold coordination site and the B cation in . Jun 12, · A systematic study of La-based perovskite-type oxides from the viewpoint of their Conventional ceramic processing techniques were used to fabricate dense ceramic samples.
is a key step necessary for the practical development of chemical looping combustion (CLC).
In this study, a series of ABO3 perovskites, where A = La, Ba, Sr, Ca. Research work on complex perovskites show that these compounds offer distinct advantages as compared with simple perovskites.g.
there are a several other compounds that show crystal structures close to the perovskite type structure. A later study of Ba2+ 2 (B3+ Nb5+)O6 systems (29) demonstrated that for a ﬁxed charge difference of 2.
a threshold in ionic radii difference lying between 5% and 17% separated compounds with B-site order from those with a random cation distribution. order has been found in hundreds of oxides. the resultant double-perovskite structure has.