Structural and dielectric properties, electron paramagnetic resonance, and defect chemistry of Pr-doped BaTiO3 ceramics

Fine-grained Pr-doped BaTiO3 ceramics (BPT) were prepared according to the nominal formula (Ba1−xPrx)Ti1−x/4O3 (0.02 ⩽ x ⩽ 0.05) using a mixed oxide method. Structure, microstructure, dielectric properties, and defect chemistry were investigated by X-ray diffraction (XRD), Raman spectroscopy, electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), and dielectric measurements. Crystal structure changed from tetragonal (0.02 ⩽ x ⩽ 0.04) to cubic (x = 0.05), accompanied by a linear decline of the c/a axial ratio with x. BPT exhibited a slight diffuse phase transition behavior and its dielectric-peak temperature (Tm) decreased rapidly at a rate of −22 °C/at.% Pr. Pr ions were substituted predominantly for Ba sites as Pr3+ and induced Ti-vacancy defects, which are evidenced by a change in unit cell volume, a rapid Tm - shifting rate, a new Raman band at ∼837 cm−1, and an EPR signal at g = 2.002. A very small number of Pr ions inevitably entered Ti sites as Pr4+, which is evidenced by a thermally accessible signal at g = 3.77 related to the preservation history of the x = 0.05 sample. The effect of electron free radicals on EPR signal is discussed. Another thermally accessible EPR signal associated with a rhombic g-tensor of the stronger g = 2.002 signal was observed. This signal is also related to the preservation history of the sample.