Oxidative layered perovskites

There is often a wide range of crystalline soHd solubiUty between end-member compositions. Additionally the ferroelectric and antiferroelectric Curie temperatures and consequent properties appear to mutate continuously with fractional cation substitution. Thus the perovskite system has a variety of extremely usehil properties. Other oxygen octahedra stmcture ferroelectrics such as lithium niobate [12031 -63-9] LiNbO, lithium tantalate [12031 -66-2] LiTaO, the tungsten bron2e stmctures, bismuth oxide layer stmctures, pyrochlore stmctures, and order—disorder-type ferroelectrics are well discussed elsewhere (4,12,22,23). 

Finally, the abatement of NO pollution by using sorbing catalytic materials [59,60] must also be cited. Several solid sorbents for NO removal (metal oxides, spinels, perovskites, double-layered cuprates, zeolites, carbonaceous materials, heteropolyacids and supported heteropolyacids) have been tested. The results are interesting, but not competitive to actual technologies. To mention that the use of sorbing materials allows... 

Many layer-perovskites with Cu as the B cation are superconductors at relatively high temperatures ( 100 K). Although the mechanism of superconductivity is not well understood, a necessary condition is that the oxidation state of the copper ion be around +2.2. In many compounds, such as the well-known YBa2Cu307 (63324) this is achieved naturally through the relaxation of... 

Depth profiles of matrix elements on Mn- and Co-perovskite layers of fuel cathodes have been measured by LA-ICP-MS in comparison to other well established surface analytical techniques (e.g., SEM-EDX).118 On perovskite layers at a spatial resolution of 100p.m a depth resolution of 100-200 nm was obtained by LA-ICP-MS. The advantages of LA-ICP-MS in comparison to other surface analytical techniques (such as XPS, AES, SIMS, SNMS, GD-OES, GDMS and SEM-EDX) are the speed, flexibility and relatively low detection limits with an easy calibration procedure. In addition, thick oxide layers can be analyzed directly and no charging effects are observed in the analysis of non-conducting thick layers. 

High-quality, pore-free microstructures of PZ - PT piezoceramic, (b) and (c), are essential for reliable, high-performance applications, e.g. composites and arrays where very small elements are cut from larger pieces (e.g. see Fig. 6.36) (d) the layer-structured bismuth titanate ferroelectric (Bi4Ti3012) Tc 650°C the crystal structure consists of perovskite layers separated by bismuth oxide layers) is exploited in high-temperature applications, including accelerometers and flow-meters (reproduced with permission of Ferroperm Piezoceramics A/S, Denmark). 

Electron microscopy of ferroelectric bismuth oxides containing perovskite layers... 

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. 

Materials of particular interest are the perovskite oxides BaTiOs-SrTiOs (BST) and PbZrOs-PbTiOs (PZT) solid solutions as well as the layered perovskites based upon SrBi2Ta209 (SBT). Since the ferroelectric effect requires... 

Organic-perovskite hybrids play an important role in the fabrication of various nanodevices as well as in elucidating their fundamental properties. Intercalation of organic components into layered perovskites can be facilitated by various techniques such as ion exchange and the exfoliation-restacking method. In addition, the electrochemical intercalation method is also favorable for intercalation of organic molecules into transition metal oxides. However, except for... 

Perovskite-related Oxides.—The perovskite-related oxides have been studied extensively in recent years because of the large variety of device applications for which these materials are suited. The interaction between structure, properties, and stoicheiometry is significant at all levels, but here we will discuss only the narrow areas where intergrowth is a dominant structural feature. We will not, therefore, consider solid solutions typified by the Pb(Zr Tii )03 ferroelectrics, and neither will we discuss the structurally complex but stoicheiometric phases related to hexagonal BaTiOj, which includes BaNiOj, which has a simple two-layer repeat in the c-direc-tion, the nine layer BaRuOj, the twelve layer Ba4Re2CoOj2, and the twenty-four layer Sr5Re20ig phase. The crystal chemistry of these phases is treated in detail by Muller and Roy. The materials we shall discuss are the two series of phases A B 0 +2 and A + B 02n+, and the bismuth titanates. Some of the anion deficient perovskites, ABO -x, will be considered in Section 5. 

The potential at which this reaction can be carried out is so high (E >1.3 V) that even noble metals are covered with an oxidic layer in fact, conducting oxides (e.g. Co-based spinels and perovskites) are often used in this process. Because of the forcing conditions, anode stability looms large, but that is another story. Many, very many mechanisms have been proposed for the reaction. Fortunately, they can be reduced to essentially two types, the same two t) es we have encountered in the case of H2 evolution vide supra), viz. the recombination of two adsorbate atoms and the reaction of an adsorbate with a solution species under the formation of an 0-0 bond ( peroxide path). The prototype of the former mechanism is that of KrasiTshikov ... 

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