Structural evolution and dielectric properties of Nd and Mn co-doped BaTiO3 ceramics

(Ba1−xNdx) (Ti0.97Mn0.03)O3 (BNTM) (x = 0.01, 0.02, 0.04, 0.06) ceramics were prepared using a conventional cold-pressing ceramic technique. The structure, valence state and dielectric properties were investigated using XRD, RS, SEM, TEM, EPR, and dielectric temperature and frequency measurements. XRD, RS analysis coupled with SEM and TEM observations indicate that the samples have a coexistence of tetragonal and hexagonal phase at room temperature as x ≤ 0.02 and become a single phase in the tetragonal as x = 0.04 and in the cubic as x = 0.06 (air-sintered, 1400 °C/12 h). It reveals that Nd3+ ions can suppress hexagonal phase effectively and benefit the formation of single-phase ceramics. Improvement of dielectric properties is accompanied by the structural evolution. Particularly a cubic ceramic with x = 0.06, the dielectric-peak temperature is found to shift to room temperature, meeting the EIA Y5V specification with tan δ < 0.04. Up to x = 0.04, the phase transition remains first order. The valence state of Mn ions was analyzed by EPR. It is found that Mn ions transform from high valence (+3 and + 4) to low valence (+2) with the increase of Nd concentration, and all of the Mn ions exist as Mn2+ when x = 0.06. The unit cell volume and dielectric-peak temperature of BNTM decrease nonlinearly with increasing x, which can be ascribed to the incorporation of Nd ions and the formation of 2NdBa·−MnTi″ donor-acceptor defect complexes.