Perovskites containing

At the other end of the conduction spectrum, many oxides have conductivities dominated by electron and positive hole contributions to the extent that some, such as Re03, SnOa and tire perovskite LaCrOs have conductivities at the level of metallic conduction. High levels of p-type semiconduction are found in some transition metal perovskites especially those containing alio-valent ions. Thus the lanthairum-based perovskites containing transition metal ions, e.g. LaMOs (M-Cr, Mn, Fe, Co, Ni) have eirlranced p-type semiconduction due to the dependence of the transition metal ion valencies on the ambient... 

Perovskites. Materials of the formula ABO3 having the per-ovskite structure (32) can be prepared in a form containing lanthanum. Some perovskites containing cobalt and strontium, LaCoOa... 

In order to understand the ferromagnetic order that is sometimes found in perovskites containing 3d4 ions, it is necessary to investigate the effect of Jahn-Teller stabilizations when there is no static, cooperative distortion of the entire lattice. Lack of a static Jahn-Teller stabilization may indicate either (1) noncooperative, static distortions or (2) removal of the ground-state degeneracy by resonance between... 

Park J-H, Woodward PM, Parise JB (1998) Predictive modeling and high pressure-high temperature synthesis of perovskites containing Ag. Chem Mater 10 3092-3100 Pasternak MP, Rozenberg GK, Machavariani GY, Naaman O, Taylor RD, Jeanloz R (1999) Breakdown of the Mott-Hubbard state in Fc203 A first-order insulator-metal transition with collapse of magnetism at 50 GPa. Phys Rev Lett 82 4663-4666... 

Lintz and Wittstock (1996) compared the results obtained for the catalytic combustion of acetone over substituted Mn perovskite containing La and Sr as A cation with those of the CuMn204 catalyst. The latter material, copper manganate, is a well-known oxidation catalyst for VOCs removal and is commercially available. Lao.sSro MnCL (64 m2 g ) was even more active than the commercial catalyst. 

As correlations have been observed, for catalytic oxidation reactions, between the activity and the electronic state of the transition metal [8], or the non stoichiometry of the perovskite [9], we have chosen, in our study, three perovskites containing cobalt in three different oxidation states, i) Co (II) in Ba2CoW06, ii) Co (III) in LaCoOs, iii) Co (IV) in BaCoOs, and we have compared their reactivity with the spinel C03O4. 

Because of their interesting magnetic properties, hybrid layered perovskites containing transition metal ions were... 

The best known examples of octahedral distortion in perovskites are Jahn-Teller distortions. These arise from the (first order) Jahn-Teller effect, which, in the broadest sense, applies to all nonlinear molecules. The Jahn-Teller theorem says that a molecule with a symmetrical atomic configuration and a degenerate electronic ground state is unstable and will distort so as to remove the electronic degeneracy. With respect to perovskite structures, the Jahn-Teller theorem applies to octahedrally coordinated transition metal B-site cations. It implies that perovskites containing ions with certain d-electron configurations (so-called Jahn-Teller ions) will have an enhanced stability when located in... 

The structural chemistry of the BaNiOj-derived hexagonal perovskites containing octahedra and trigonal prisms is surveyed in the following ... 

Many other perovskites containing mixed valence cations behave in a similar way, and these can be modified with A- or B-site substitutions in order to improve either aspects of stabihty or conductivity. For example, the perovskite SrFej Sc Oj shows the same conductivity dependence as SrjFe Og ... 

Cation charge ordering may also occur in a perovskite containing cations with two different charge states, and this can be instmmental in preventing the formation of a metallic phase where one might be expected. This has been well documented in the... 

Many technically important materials prepared by sol-gel processing, such as perovskites, contain more than one kind of metal atom. The first approach is to employ precursor mixtures, which can be either mixtures of metal alkoxides or mixtures of one or more metal alkoxides and metal salts. The co-hydrolysis and co-condensation of different precursors may result in inhomogeneous materials because of their different reaction rates and the fact that the formation of a gel is a kinetically controlled process. The inhomogeneity can be on any length scale from the nanometer range up to macroscopic phase separation. Common methods to solve this problem and to obtain homogeneous (mixed on a nanometer scale) heterometallic gels from precursor... 

As alternative mixes of OCs have been used to evaluate if advantages of OCs could be combined and the drawbacks be reduced [9]. For example, the reactivity and the fuel conversion could be increased, the amount of expensive or toxic material decreased and the strength of the particles increased. Studies have been conducted with many different combinations (Cu/Fe, Cu/Ni, Fe/Ni, Co/Ni, Fe/Mn), but have not resulted in an application on a larger scale until now [9]. Perovskite structures have been proposed as well, which might also be applicable for the CLOU process in case perovskite contains Mn-Ca-O [29]. 

With regards to similar distortions, it should be emphasized that displacements of the A and B cations from the centers of corresponding polyhedra which lead to dipole moments are remarkable, as these produce ferroelectricity and related famous phenomena. Perovskites containing high-charge B cations such as Ti, Zf... 

---