Microstructure of six-pointed starlike anatase aggregates

作者：Ban Takayuki^*; Nakatani Tomohiko; Uehara Yasufumi; Ohya Yutaka

来源：Crystal Growth & Design, 2008, 8(3): 935-940.

DOI：10.1021/cg7008072

Six-pointed starlike anatase aggregates were synthesized hydrothermally from aqueous sots of tetramethylammonium titanate colloids having a lepidocrocite-type layered structure. Their microstructure was examined by transmission electron microscopy (TEM). The star-shaped aggregates had a 6-fold symmetry similar to hexagonal crystals, although anatase has a tetragonal lattice. Acicular anatase nanocrystals extending along the c-axis direction were aligned parallel to each other to form one-half of the aggregate arm and were connected with the acicular crystals in the other half on the 1112) plane by twinning. The fact that the angle between the (112) and (11 (2) over bar) planes is about 60 degrees contributes to the 6-fold symmetry of the starlike aggregates. In a higher resolution TEM image, fringe contrast was observed normal to the c-axis of the anatase crystals. The interval was close to the basal spacing of the original layered tetramethylammonium titanate, although the X-ray diffraction (XRD) pattern did not show any peaks of the titanate. It was inferred that the anisotropic self-assembly of the layered-titanate colloids, their topotactic structural conversion to anatase, and the twin formation of anatase crystals play important roles in the formation of the acicular anatase crystals and the star-shaped aggregates.

• 出版日期2008-3