Defect evolution and effect on structure and electric properties of A/B site Sm doped BaTiO3 sintered in different atmospheres

BaTiO3 ceramics doped with different contents of Sm (0.5–7 mol%) are prepared by a homogeneous precipitation method and sintered in air (A-xSm) and reducing (R-xSm) atmosphere respectively. With the increase of doping amount, the phase structure of Sm-doped BaTiO3 ceramics gradually changes from tetragonal phase to cubic phase, and the cubic phase is stronger in R-xSm. In the air atmosphere, Sm ions preferentially replace Ba sites as donors at low doping concentration, which is easy to convert Ti4+ ions into Ti3+ ions, resulting high dielectric constant (>104) and semiconductor like properties. As the doping amount increases, Sm ions start to replace Ti sites as acceptors to generate oxygen vacancies, which capture the electrons generated by donor doping, thus decreasing the percentage of Ti3+ ions. As a result, the dielectric loss and permittivity are decreased, and the electrical insulation properties of A-xSm ceramics are gradually improved. However, in the reducing atmosphere, oxygen atoms in the lattice are easy to escape, resulting in many oxygen vacancies and free electrons. The increase of oxygen vacancy inhibits the substitution of Sm ion to Ti site, and the free electron leads to the increase the percentage of Ti3+ ions and R-xSm ceramics exhibit semiconductor like properties. Thermally stimulated depolarization currents (TSDC) testing verified that oxygen vacancies of A-xSm ceramics mainly capture space charges, and a small part of oxygen vacancies form defective dipoles [2SmTi′−VO..]. The complex impedance test shows that the change of resistivity of A-xSm ceramics is mainly closed to the influence of Sm doping on the grain not grain boundary of BaTiO3 ceramic.