Materials Discovery by Crystal Growth
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Materials Discovery by Crystal Growth Samuel J. Mugavero III, William R. Gemmill, and Hans-Conrad zur Loye Chemistry & Biochemistry, University of South Carolina, 631 Sumter Street, Columbia, SC, 29208 ABSTRACT The growth of new phases out of high temperature hydroxide solutions as a means of discovering new materials is discussed. We have succeeded in solubilizing rare earth cations and platinum group metal cations in molten hydroxides and have grown single crystals with a large number of new compositions and new structure types. The use of sealed silver tubes has enabled us to control the water content and, hence, the acidity of the hydroxide melts, and thereby to grow crystals via slow cooling. The synthetic conditions and structures of several new oxides including Ln1-xNa1+xIrO4 (Ln = Gd-Er, Y; x = 0.04-0.26), Ln3RuO7 (Ln = La, Sm, Eu), LnNaPd6O8 (Ln = Tb-Lu, Y) and La9RbIr4O24 are presented. INTRODUCTION Recent interest in the synthesis, characterization, and physical property measurement of complex metal oxides of platinum group containing metals has been ever increasing. Several research groups have been participating in these efforts yielding a wealth of new compounds with structures as diverse as their physical properties. Traditionally, such materials are prepared as polycrystalline powders via solid-state reaction of the elements, binary oxides, or precursor reagents at high temperatures. Although extremely useful in preparing sufficient quantities for physical property measurement, such synthetic techniques typically yield the thermodynamically favored product, thus setting a limit on what materials can be isolated. However, this limitation can be circumvented by the use of alternative synthetic methods that grant access to phases that may not have been isolated via conventional means, offering opportunity for the discovery of new materials. An alternative method of material preparation is single crystal growth from high temperature solutions. This well-established method is exceptionally suited for oxide crystal growth, for there exist a multitude of published compositions containing elements from nearly every section of the periodic table. [1] In addition, crystal growth from solution has advantages over standard ceramic methods such as; enhanced mixing of reagents which facilitates reaction, possibility of controlling the nature of the species in solution (i.e. oxidation state), and most importantly the ability to employ single crystal X-ray diffraction for accurate structure solution of complex materials. Many high temperature solutions have been utilized in the crystal growth of oxide crystals including alkali and alkaline earth carbonates, halides, peroxides, superoxides, and hydroxides. [2-7] For more than a decade the zur Loye group has focused on crystal growth of complex oxides containing platinum group metals from high temperature solutions. Our initial efforts in the crystal growth of platinum group metal oxides utilized alkaline earth carbonates as a solvent of crystallization
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