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

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 °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 °C. Raman features characteristic of the stable Aurivillius nanocrystals can be detected after thermal treatment at 550 °C, while using X-ray diffraction the crystallization of the Bi-layered perovskite phase is observed only after treatment at 625 °C or higher temperatures. Both X-ray and Raman scattering detected single phase nanocrystallites with Aurivillius structure above 650 °C. The distinctive Raman features of the different SrBi2Nb2O9 nanocrystallites and its evolution with thermal treatment is presented.