Electron Paramagnetic Resonance Study on Oxygen Vacancies and Site Occupations in Mg-Doped BaTiO(3) Ceramics

Nominal (Ba(1−x)Mg(x))TiO(3) (x = 0.015) (BM1T) and (Ba(1−x)Mg(x))TiO(3) (x = 0.03–0.20) (BMT) ceramics were prepared by the mixed-oxide route at sintering temperatures (T(s)) of 1200−1400 °C and 1200 °C, respectively. The solubility limit of Mg(2+) in BMT was determined by XRD to be x = 0.05, and evidence was found for occupation of the A site by Mg(2+). Electron paramagnetic resonance (EPR) was employed as a key technique to investigate the effect of T(s) on oxygen vacancies in BM1T. The structure of BM1T changed from pseudocubic at T(s) = 1200 °C to tetragonal at 1300 °C to mixed phases of hexagonal and tetragonal at 1400 °C. When T(s) ≥ 1300 °C, a g = 1.956 EPR signal was observed at T = −188 °C and assigned as ionized oxygen vacancies. Mg(2+) exhibited amphoteric behavior of substituting for the double cation sites. When T(s) = 1400 °C, B-site Mg(2+) and oxygen vacancies mainly existed in the hexagonal phase and A-site Mg(2+) was dominant in the tetragonal phase. The higher tan δ was attributed to the higher concentrations of oxygen vacancies and Ti(3+) in the hexagonal phase.