Dielectric relaxation in layer-structured SrBi_2−xGd_xNb₂O₉ (x = 0.0, 0.4, 0.6, and 0.8) lead-free ceramics

The gadolinium (Gd³⁺)-doped SrBi₂Nb₂O₉ (SBN) ceramics with the chemical formula SrBi_2−xGd_xNb₂O₉ (x = 0.0, 0.4, 0.6, and 0.8) have been prepared through traditional solid-state sintering method. X-ray diffraction reveals a single-phase-layered perovskite structure for all compositions with shrinkage of the unit cell of SBN. The plate-like morphology revealed from SEM is symbolic of the characteristic Aurivillius phase of ceramics. Shifting of Raman phonon modes indicates the reduced rattling space of NbO₆ octahedral with an increase in Gd concentration. The dielectric properties of all compositions are studied as a function of temperature (RT—500 °C) over the frequency range (50 Hz to 1 MHz). Softening the lowest frequency mode with increasing x in SBGN shows the transition from ferroelectric to paraelectric at room temperature (RT). The flattening of dielectric permittivity and low dielectric loss is observed in SBN and gadolinium-modified SBN (SBGN) ceramic samples at RT. The phase transition becomes diffused and transition temperature gets shifted from 430 to 330 °C with an increase in gadolinium concentration at higher frequencies. The increase in broadness with an increase in frequency suggests that the presentation materials are of ferroelectric relaxor type. The degree of relaxor behavior (γ) increases from 1.05 for x = 0.0 to 1.57 for x = 0.8. The relaxor behavior along with diffuseness was noticed in the fabricated ceramics.