Generalized nonaqueous sol-gel synthesis of different transition-metal niobate nanocrystals and analysis ofthe growth mechanism

Abstract

A general nonaqueous route for the synthesis of phase-pure transition-metal niobate (InNbO4, MnNb2O6, and YNbO 4) nanocrystals was developed based on the one-pot solvothermal reaction of niobium chloride and the corresponding transition-metal acetylacetonates in benzyl alcohol at 200°C. All samples were carefully characterized by XRD, TEM, HRTEM, and energy-dispersive X-ray (EDX) analysis. The crystallization mechanism of these niobate nanocrystals points to a two-step pathway. First, metal hydroxide crystals and amorphous niobium oxide are formed. Second, metal niobate nanocrystals are generated from the intermediates by a dissolution-recrystallization mechanism. The reaction mechanisms, that is, the processes responsible for the oxygen supply for oxide formation, were found to be rather complex and involve niobium-mediated ether elimination as the main pathway, accompanied by solvolysis of the acetylacetonate ligands and benzylation reactions. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.