Structural, electrical, magnetic and optical properties of BaTi_1−x(Ni_1/2Nb_1/2)_xO₃ ceramics

In this work, we have investigated the structural, electrical, magnetic and optical properties of Ni–Nb co-doped BaTiO₃ ceramics. The compositions of BaTi_1−x(Ni_1/2Nb_1/2)_xO₃ (0 ≤ x ≤ 0.1) were prepared through conventional solid-state reaction method. All the samples exhibit a gradual phase transition behavior from the tetragonal to a cubic structure with the increase in the Ni–Nb co-doping concentration. SEM and EDAX characterizations show that the ceramic samples have good crystallinity and uniform doping element Ni–Nb distribution. The temperature dependence of the dielectric constant reveals that Curie temperature gradually decreased with an increase in Ni²⁺ and Nb⁵⁺ concentrations. The ferroelectric studies show these doping samples exhibit a decreasing ferroelectric property with the increasing level of doping. The decrease in Curie temperature and the weakening of ferroelectricity can be attributed to the transformation of the crystal structure from the tetragonal phase to the cubic phase. Magnetic measurements show that the formation of the F-center makes the sample have ferromagnetic order at room temperature. By studying the effects of different Ni–Nb doping concentrations on the ferroelectricity and ferromagnetism of BaTiO₃, it was found that among all samples, when the doping concentration x = 0.08, the ceramic samples showed the best multiferroicity. Moreover, the band gap of these samples is significantly reduced due to the introduction of impurity levels. These results indicate the potential application of Ni–Nb co-doped BaTiO₃ in multiferroic devices.