Lead complexes mixed-metal

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. 

Bismuth trioxide forms numerous, complex, mixed oxides of varying composition when fused with CaO, SrO, BaO, and PbO. If high purity bismuth, lead, and copper oxides and strontium and calcium carbonates are mixed together with metal ratios Bi Pb Sn Ca Cu = 1.9 0.4 2 2 3 or 1.95 0.6 2 2 3 and calcined at 800—835°C, the resulting materials have the nominal composition Bi PbQ4Sr2Ca2Cu20 and Bi 25PbQgSr2Ca2Cu20 and become superconducting at about 110 K (25). 

The continued development of new single-source molecular precursors should lead to increasingly complex mixed-element oxides with novel properties. Continued work with grafting methods will provide access to novel surface structures that may prove useful for catalytic apphcations. Use of molecular precursors for the generation of metal nanoparticles supported on various oxide supports is another area that shows promise. We expect that the thermolytic molecular precursor methods outlined here will contribute significantly to the development of new generations of advanced materials with tailored properties, and that it will continue to provide access to catalytic materials with improved performance. 

Many additional complexities can occur in reactions of this type due to the presence of more than one complex in solution and to metal-buffer interactions which can lead to additional metal equilibria involving the buffer anion and even to mixed ligand complex formation. 

In nonreactive molten salts, on the other hand, flux components are not incorporated into the product phase. Here, the molten salt acts more in the classical sense as a reagent to promote the reaction at a lower temperature than would be required by the ceramic, or direct, route (Section 5.2). This is accomplished by two attributes of molten salts an acid-base equilibrium that enables the general dissolution-recrystallization of metal oxides and a highly electropositive (oxidizing) environment that stabilizes the highest oxidation state of many transition metals (Gopalakrishnan, 1995), which can lead to mixed valency. A plethora of complex transition metal oxides have been synthesized in nonreactive molten alkali metal hydroxides, carbonates, and hypochlorites. Examples of such molten salt routes to mixed transition metal oxides include (Rao and Raveau, 1998) ... 

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