Formation and micro-Raman spectroscopic study of Aurivilius and fluorite-type SrBi2Nb2O9 nanocrystallites obtained using an 'amorphous citrate' route

Abstract

The crystallization of a SrBi2Nb2O9 gel-glass obtained using the amorphous citrate method was studied by micro-Raman scattering, X-ray diffraction, and electron microscopy techniques. A citric acid-ethanolamine gel with the stoichiometric proportion of the metallic cations was prepared as polymeric precursor and calcined to obtain the amorphous complex. Nanocrystallites with a metastable fluorite-type structure nucleate from the amorphous complex below 500 degrees C, as shown by X-ray scattering and confirmed by electron microscopy. The morphological study by scanning electron microscopy revealed the nucleation of nanocrystals in the glass-like amorphous powder after thermal treatment at 500 degrees C. Raman features characteristic of the stable Aurivillius nanocrystals can be detected after thermal treatment at 550 degrees C while using X-ray diffraction the crystallization of the Bi-layered perovskite phase is observed only after treatment at 625 degrees C or higher temperatures. Both X-ray and Raman scattering detected single phase nanocrystallites with Aurivillius structure above 650 degrees C. The distinctive Raman features of the different SrBi2Nb2O9 nanocrystallites and its evolution with thermal treatment is presented.