Characterization of Voids in Rutile Nanoparticles by Transmission Electron Microscopy
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ABSTRACT Rutile nanoparticles containing voids or cavities have been characterized using transmission electron microscopy. The general morphology of the voids has been determined from images of nanoparticles in different orientations. In general, the longest dimension is along the c axis of rutile. Many of the voids show a prismatic morphology with dipyramid terminations. The prism consists of primarily four {110} faces with rounded or faceted comers between the primary faces. The pyramidal terminations can appear ovoid or faceted. A major facet plane of the pyramids is (101). A model consistent with the morphology of many voids in rutile nanoparticles is proposed. INTRODUCTION Characterization of the morphology and microstructures of nanoparticles is important in understanding the properties of these materials and for the development of potential new applications of the materials. In this study, TiO 2 nanoparticles containing voids are characterized. TiO 2 nanoparticles have been the subject of considerable interest in part because TiO 2 can be used as a photocatalyst for dissociation of water, organic compounds and other compounds [1-3]. It can also be used to form ceramic, microporous
membranes [4], to decrease the sintering temperature of titania ceramics [5], and, potentially, as coatings on surgical implants [6]. In previous work [7], it was shown that some rutile nanoparticles contain central inclusions. These inclusions were characterized as voids using electron holography. Similar cavities have been noted in palladium nanoparticles [8-10]. Faceted cavities have also been found in larger-grained material and have been termed negative crystals. Negative crystals form in P-V 4As 3 upon exposure to the electron beam of a transmission electron microscope (TEM) [11] and have been found in TiO 2 (B) crystals formed from K2 Ti4O9 precursor material [12]. Faceted cavities in sapphire form at the tips of indentation cracks during annealing [13]. The morphology of cavities in materials is of interest in determining volume changes if the host material is a transformation product from an unknown precursor. The morphology is also of interest in studies of the surface energies of crystals [13]. The morphology of faceted cavities in bulk materials has been studied by preparing the sample perpendicular to crystallographic directions of interest so that expected facets are viewed edge on [ 13]. Determination of morphology of cavities in nanoparticles is less straightforward as the nanoparticles are typically randomly oriented on a transmission
467 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
electron microscope (TEM) grid. TEM imaging and electron holography has been used to show the presence of facets in palladium nanoparticles [8-10], however, the morphology of the faceted cavities in the palladium nanoparticles has not been fully described. In this work, the morphology of the rutile material defining the voids is characterized using selected area electron diffraction (SAED) and imaging. A thr
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