Formation of Nanoneedles and Nanoplatelets of KNbO3Perovskite during Templated Crystallization of the Precursor Gel

Highly anisotropic nanocrystallites in the form of nanoneedles and nanoplatelets of KNbO 3 perovskite were prepared by crystallization of the amorphous gel. The gel was prepared by the polymerizable-complex method based on the Pechini-type reaction route. The nanoneedles were typically 50 nm thick and approximately 10 μm long and had surfaces parallel to the {100} planes of the pseudocubic perovskite. The formation of these pseudocubic KNbO 3 perovskite crystallites of an unusual and highly anisotropic shape was studied by electron microscopy in combination with X-ray diffractometry and thermal analyses. A layer-structured compound, K 4 Nb 6 O 17, appeared as the first crystalline phase during the heating of the amorphous precursor gel at temperatures around 490 °C. When this compound reacts to form the cubic perovskite at higher temperatures (around 540 °C), its highly anisotropic, layered structure defines the anisotropic shape of the product.