Phase transition behavior and ferroelectric and vibrational properties of (Na0.5Bi0.5)1−xBaxTi1−x(Fe0.5Nb0.5)xO3 ceramics

(Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 (NBT–BFN) lead-free ceramics with different compositions (0 ≤ x ≤ 0.1) were synthesized by the conventional solid-state reaction method and characterized by X-ray diffraction, dielectric and ferroelectric measurements, and also Raman spectroscopy. X-ray diffraction showed the presence of a single phase. The evolution of Raman spectra was recorded as a function of the chemical composition (0 ≤ x ≤ 0.1) and temperature (from 83 to 763 K). The general features of Raman spectra of the different compositions were almost similar with only subtle changes that can be attributed to the ferroelectric order rather than the structural phase transition. The complementarity between micro-Raman spectroscopy and macro-dielectric results was highlighted. Evidence of ferroelectric–antiferroelectric transition (Td) and the transition temperature (Tm) was determined via Raman spectroscopic characterization. Raman scattering revealed that both substitutions on A and B sites pretreated local octahedra and resulted in localized non-polar regions that improved piezoelectric response. A detailed analysis of the temperature dependence of polarization–electric field (P–E) loops was performed for (Na0.5Bi0.5)0.925Ba0.075Ti0.925(Fe0.5Nb0.5)0.075O3. This composition showed a ferroelectric–antiferroelectric phase transition around Td. This ceramic provides enhanced piezoelectric performance at room temperature compared to undoped NBT: the piezoelectric constant was d31 = 16.98 pC/N and the electromechanical coupling factor was kp = 0.278%.