RESUMEN
Recent advances in exploiting microwave radiation in the topochemical modification of layered oxide perovskites are presented. Such methods work well for rapid bulk synthetic steps used in the production of novel inorganic-organic hybrids (protonation, grafting, intercalation, and in situ click reactions), exfoliation to produce dispersed nanosheets, and post-exfoliation processing to rapidly vary nanosheet surface groups. Compared to traditional methods that often take days, microwave methods can produce quality products in as little as 1-2 h.
RESUMEN
The construction of two-dimensional (2D) copper halide networks within a variety of perovskite hosts by a low-temperature topochemical method is demonstrated. Ion exchange between some layered perovskite oxides of the type A'[An - 1(M,M')nO3n + 1] (A' = alkali metal, H, NH4; A = alkaline earth, rare earth, or Bi; M,M' = Nb, Ta, Ti; n = 2, 3) with CuX2 (X = Cl, Br) results in the oxyhalides (CuX)[An - 1(M,M')nO3n + 1]. Rietveld refinements from X-ray powder diffraction data show that the structures of these new copper oxyhalides contain edge-sharing CuO2X4 octahedra sandwiched between the M/M'O6 octahedra of the perovskite slabs. The compounds are low-temperature phases that decompose well below 700 degrees C. The copper oxyhalides exhibit antiferromagnetic ordering resulting from the magnetic exchange interactions within the planar Cu-X networks.
RESUMEN
Precursor reactions based on metathetical (exchange) pathways have been found to be an effective synthetic route for the preparation of a large number of materials. These solid-solid reactions are extremely rapid (typically less than 1 second) and often can be initiated at or near room temperature. They are potentially useful for controlling product particle size and for preparing highquality cationic or anionic solid solutions. The frequently self-propagating and sometimes explosive behavior exhibited by these reactions can be attributed to the large amount of heat they release. As a consequence, thermodynamic considerations can be used to help select the best set of precursors as judged from reaction enthalpies. The factors that influence these reactions are illustrated by a discussion of MoS(2), ZrN, MoSi(2), and GaAs, examples of the many compounds accessible by this synthetic route.
RESUMEN
A major barrier to use of new measurement methodologies in behavioral research has been the difficulties encountered in collecting individual judgements. Balanced incomplete block design (BIBD) procedures offer enormous flexibility in the way judgmental data may be collected. The advantages and disadvantages of BIBDs are clarified and their use is demonstrated with an empirical example. A procedure for reducing data of this type to analyzable form is proposed and an analytical approach that is appropriate for the resulting data is illustrated.