Niobium oxide (Nb 2 O 5 ) is an interesting active material for technologies ranging from catalysis and sensors to energy storage and electrochromic devices owing to its unique optical, electronic, and electrochemical properties. These properties vary between different phases and morphologies in the Nb 2 O 5 system, but systematic studies that correlate properties to phase and morphology are limited by current synthetic methods, which require postsynthetic high temperature treatments and suffer from a lack of direct and precise control over morphology, crystal structure, and stoichiometry. Here, we report a heat-up colloidal synthesis method that produces orthorhombic Nb 2 O 5 nanorods 1 nm in width by 31 nm in length that preferentially grow along the [001] direction. The synthesis is based on aminolysis of niobium oleate in octadecene, and nanorods are formed through three distinct steps: aminolysis-driven formation of niobium oxo clusters, condensation into amorphous Nb 2 O 5 seeds below the reaction temperature (240 °C, under atmospheric pressure), and crystallization and growth of Nb 2 O 5 nanorods. We investigated the electrochromic behavior of nanorod thin films upon Li + intercalation and observed predominantly near-infrared coloration, fast switching kinetics, and durability for at least 500 charge−discharge cycles.

Understanding growth mechanisms and the role of surface functionalization is of key importance to control shape and morphology of nanoparticles and their properties. Here, we describe the growth mechanism and the effect of hydrothermal synthesis parameters (pH, time and precursor/functionalization agent ratio) during in situ functionalization of anatase TiO2 nanoparticles with 3-aminopropyltriethoxysilane. Elongated crystallographically oriented TiO2 nanoparticles were formed by oriented attachment mechanism in addition to spherical nanoparticles. The growth mechanism is determined by a combination of ex situ techniques such as high-resolution transmission electron microscopy combined with in situ synchrotron X-ray diffraction and density functional theory calculations. Oriented attachment induced by the functionalization agent is shown to be the origin of the elongation of the nanoparticles, as only spherical nanoparticles were formed in the absence of surface functionalization. Finally, it was shown that the amount and the size of the elongated nanoparticles can be tuned by adjusting pH.

Hydrothermal synthesis is a well-established method to produce complex oxides, and is a potential interesting approach to synthesize stoichiometric lead-free piezoelectric K 0.5 Na 0.5 NbO 3. Due to challenges in obtaining the desired stoichiometry of this material, more knowledge is needed on how the end members, KNbO 3 and NaNbO 3 , are nucleating and growing. Here we report on the formation mechanisms and growth during hydrothermal synthesis of KNbO 3 and NaNbO 3 by in situ synchrotron powder X-ray diffraction. We show that tetragonal KNbO 3 crystallites form from

In situ monitoring of the formation of crystalline phases during conventional hydrothermal synthesis is experimentally challenging. Here, we report an in situ time-resolved synchrotron X-ray diffraction study during hydrothermal synthesis of NaNbO 3 using a high-pressure custom-made capillary cell penetrable to X-rays. The high time resolution (0.1 s) revealed a sequence of transient intermediate phases, including several unknown phases, before the final perovskite NaNbO 3 was formed. These new findings highlight the complexity of the hydrothermal synthesis of NaNbO 3 and demonstrate the potential for obtaining in-depth knowledge of the reactions taking place by time-resolved in situ X-ray diffraction.