Electron Paramagnetic Resonance Study on Oxygen Vacancies and Site Occupations in Mg-Doped BaTiO₃ Ceramics

• Main Authors: Dayong Lu, Yongshun Zheng, Longfei Yuan
• Format: Article
• Language: English
• Published: MDPI AG 2019-05-01
• Series: Materials
• Subjects: barium titanate ceramics; dielectric properties; oxygen vacancies; site occupations; electron paramagnetic resonance
• Online Access: https://www.mdpi.com/1996-1944/12/9/1525

Nominal (Ba_1&#8722;xMg_x)TiO₃ (<i>x</i> = 0.015) (BM1T) and (Ba_1&#8722;xMg_x)TiO₃ (<i>x</i> = 0.03&#8722;0.20) (BMT) ceramics were prepared by the mixed-oxide route at sintering temperatures (T_s) of 1200&#8722;1400 &#176;C and 1200 &#176;C, respectively. The solubility limit of Mg²⁺ in BMT was determined by XRD to be <i>x</i> = 0.05, and evidence was found for occupation of the A site by Mg²⁺. 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 <i>T</i>_s = 1200 &#176;C to tetragonal at 1300 &#176;C to mixed phases of hexagonal and tetragonal at 1400 &#176;C. When <i>T</i>_s &#8805; 1300 &#176;C, a<i> g </i>= 1.956 EPR signal was observed at<i> T</i> = &#8722;188 &#176;C and assigned as ionized oxygen vacancies. Mg²⁺ exhibited amphoteric behavior of substituting for the double cation sites. When <i>T</i>_s = 1400 &#176;C, B-site Mg²⁺ and oxygen vacancies mainly existed in the hexagonal phase and A-site Mg²⁺ was dominant in the tetragonal phase. The higher tan <i>&#948;</i> was attributed to the higher concentrations of oxygen vacancies and Ti³⁺ in the hexagonal phase.