Electron spin resonance investigations and compensation mechanism of europium-doped barium titanate ceramics

The electron spin resonance (ESR) technique was employed to investigate the point defects and evidence of Eu2+ in Eu-doped barium titanate (EBT) ceramics sintered in air according to the formula (Ba1-xEux)Ti1-x/O-8(3). The charge equilibrium compensation mechanism was discussed on the basis of ESR with the aid of X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques. Eu is incorporated into Ba sites of BaTiO3 as Eu3+ up to x = 0.02 and as mixed Eu2+/Eu3+ at x = 0.03, which is evidenced by Eu3+-induced Ti-vacancy defects with g = 2.004 and a broad Eu2+ signal with g = 1.98, and a single-phase tetragonal perovskite structure can be retained. When x >= 0.04, it is concluded that high density and low porosity in highly insulating and fine-grained EBT ceramics originate from the coexistence of mixed Eu2+/Eu3+; in particular, the increase in the proportion of Eu2+ in the perovskite phase increases ceramic density, but is accompanied by emergence of the Eu2Ti2O7 phase.