Effects of (In + Nb) Co-Doping on the Microstructure and Electrical Properties of Bi 0.5 Na 0.5 TiO 3 Ceramics

(In + Nb) co-doped Bi _0.5 Na _0.5 TiO ₃ (BNT) ceramics ( x  = 0.00, 0.01, 0.02, 0.04, 0.06, 0.08) were prepared via the conventional solid-state method. With increasing doping level, the crystal structure transformed gradually from rhombohedral to tetragonal phase. SEM observations revealed dense microstructures, and the average grain sizes increased first and then decreased with increasing doping levels. Raman spectroscopy reveals an increase in oxygen vacancy concentration, a weakening of Na–O bond polarization, and an increase in the proportion of the tetragonal phase in highly doped samples. XPS analysis confirmed the coexistence of Ti ³⁺ and defect oxygen species, with Ti ³⁺ showing a slight decrease and defect oxygen a marked increase as doping increased. With increasing doping concentration, the dielectric constant and dielectric loss of the ceramics gradually decrease, while the Curie temperature increases first and then decreases, and the depolarization temperature exhibits a decreasing trend. The optimal performance is achieved at x  = 0.01. Moderate In/Nb co-doping is beneficial for enhancing the pyroelectric properties of the ceramics, and this improvement is primarily associated with variations in oxygen vacancies, changes in Ti ³⁺ concentration, and the formation of defect dipoles.