Simple perovskite-type oxid

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,... 

One category of dense proton conducting membranes that has received considerable attention in the preceding decade is proton conducting perovskite type oxide ceramics [4-6]. The stoichiometric chemical composition of perovskites is represented as ABO3, where A is a divalent ion (A +) such as calcium, magnesium, barium or strontium and B is a tetravalent ion (B +) such as cerium or zirconium. Although simple perovskites such as barium cerate (BaCeOs) and strontium cerate... 

The mobihty of protons is not only very sensitive toward reduction of the crystallographic symmetry but also toward local structural and chemical perturbations induced by the aeeeptor dopant or by mixed occupaney on the B site. To allow for the formation of protonic defects by dissociative absorption of water, perovskite-type oxides are eommonly doped with aliovalent ions (aeeeptor dopants) matching the ionie radius of the B-site cation (e.g., In for Zr" ). Indeed, this simple concept has been proven successful, e.g., for oxide ion conductors (Sc-doped zirconia shows higher oxide ion eonduetivity than... 

Teraoka et al. [15] also reported that Co, Mn, and Fe perovskite-type and Cu-based I<2NiF4-type oxides (all with La partially substituted by alkaline metal or alkaline earth metal cations) catalyze the simultaneous removal of NO and diesel soot particulates and that these perovskite-related oxides are superior to transition metal simple oxides and Pt/Al203 with regard to their selectivity toward NO reduction. 

Oxide ion conductors with the perovskite structure mentioned above belong to so-called single perovskites, which can be expressed as the simple form, ABO3. Besides these, there are different types of perovskite-related oxides and some of them are known to show oxide ion conduction. One of them is Brownmillerite, Ba2ln205. This composition can be written as Baln02.5, and... 

Various substituted lanthanum manganates having the perovskite ABO3-type structure, as well as La2Cu04 and simple copper oxides are studied. In the present study, are reported the synthesis, characterization of the various phases and catalytic test results. 

Despite the success of this simple picture, not all B-site cations with partially filled d orbitals give rise to metallic perovskites, and many are antiferromagnetic (AFM) insulators. This dilemma was resolved in the middle of the twentieth century with respect to transition metal oxides by assuming that electron correlation, taking the form of Coulomb repulsion between electrons, split the partly filled 3d band into a filled and an empty sub-band, with a band gap between the two. This gap is the Hubbard or Mott-Hubbard gap, denoted by U, and the compounds that display this type of behaviour are called Mott insulators. 

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