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

A general nonaqueous route for the synthesis of phase-pure transition-metal niobate (InNbO4, MnNb2O6, and YNbO4) nanocrystals was developed based on the one-pot solvothermal reaction of niobium chloride and the corresponding transition-metal acetylacetonates in benzyl alcohol at 200 degrees 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.