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Abstract: Nanocrystalline NaNbO3 and NaTaO3 have been synthesized by the reverse micellar technique for the first time. The particle size of NaNbO3 was found to be 18nm while that of NaTaO3 was found to be 40nm (much smaller size than most of the earlier reports on NaTaO3). Rietveld refinement of X-ray diffraction data and Raman spectroscopy confirm that the nanoparticles of NaNbO3 and NaTaO3 have orthorhombically distorted structures with Pmc21 and Pbnm space groups, respectively. The dielectric constant at 25°C of NaNbO3 and NaTaO3 was found to be 209 and 147 at 1kHz, respectively. The antiferroelectric transition in NaNbO3 shifts to lower temperature (325°C) in the nanocrystalline solid. [Copyright &y& Elsevier]

The three-dimensional structure of nanocrystalline magnesium ferrite, MgFe2O4, prepared by ball milling, has been determined using synchrotron radiation powder diffraction and employing both Rietveld and atomic pair distribution function (PDF) analysis. The nanocrystalline ferrite exhibits a very limited structural coherence length and a high degree of structural disorder. Nevertheless, the nanoferrite possesses a very well defined local atomic ordering that may be described in terms of a spinel-type structure with Mg2+ and Fe3+ ions almost randomly distributed over its tetrahedral and octahedral sites. The new structural information helps explain the material's unusual magnetic properties. [ABSTRACT FROM AUTHOR]

The detailed understanding of the crystal structure and microstructure of nanomaterials is useful to predict the properties of nanomaterials. SnO2 nanocrystals of different shapes like particles, spheres, rods and pyramids are chemically synthesized. Here, we report the crystal structure and microstructure of SnO2 nanocrystals of different morphologies using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). It is interesting to note that the tetragonal phase is found in particle, sphere and rod shaped SnO2 nanocrystals and pyramid shaped nanocrystals are composed of two types of orthorhombic phases. The Rietveld method has been used for refining simultaneously the atomic structure and microstructure of different SnO2 nanocrystals, and the growth mechanisms in different shapes are found to be different due to different preferential growth. Structural defects such as oxygen vacancies, deformation of unit cell and more importantly texturing effects are associated with change in bond length, bond angle and crystallite morphology. Size and lattice strain of different kinds of SnO2 nanocrystals are also studied in detail by using the Rietveld method of analysis and transmission electron microscopy (TEM). [ABSTRACT FROM AUTHOR]