Chemical and structural analysis related to defects in nanocrystalline Ba1−xSrxTiO3 grown via hydrothermal sol–gel

The chemical and structural properties of Ba1−xSrxTiO3 (BST, x=0–1) nanoparticles synthesised via sol–gel–hydrothermal were analysed. Two types of salts of Ba (BaCl2 and Ba(OH)2) and Sr (SrCl2 and Sr(OH)2) as starting reactants were used to compare two synthesis methods. Chemical characterisation and oxidation states were obtained using X-ray photoelectron spectroscopy. Structural information was acquired by Raman spectroscopy, and calculations to obtain theoretical Raman spectra associated with the different formed phases of BST were performed for comparison. The results were consistent with the presence of oxygen vacancies in all of the compounds synthesised, but the use of hydroxide salts introduced a minor concentration of oxygen vacancies into the BST compounds. In addition, the presence of oxygen vacancies produced an increase of the intensity of first-order modes of vibration and a minor oxidation state of the Ti atom in the structure. Finally, the oxygen vacancies produced a distortion of the structure, inducing the existence of the non-perovskite phase.