Dielectric relaxation in layer-structured SrBi2− xGdxNb2O9 (x= 0.0, 0.4, 0.6, and 0.8) lead-free ceramics

The Gadolinium (Gd 3+ ) doped SrBi 2 Nb 2 O 9 (SBN) ceramics with the chemical formula SrBi 2-x Gd x Nb 2 O 9 (x = 0.0, 0.4, 0.6 and 0.8) have been prepared through traditional solid-state sintering method. X-ray diffraction reveals that 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 characteristic Aurivillius phase of ceramics. Shifting of Raman phonon modes indicates the reduced
rattling space of NbO 6 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 - 1 MHz). Softening lowest frequency mode with increasing x in SBGN shows the transition from ferroelectric to para electric at room temperature. The flattening of dielectric permittivity and low dielectric loss are
observed in SBN and gadolinium modified SBN (SBGN) ceramic samples at room temperature, which are desirable features to suit for Non-volatile Fe RAM applications. The phase transition becomes diffused and transition temperature gets shifted from
430 ˚C – 330 ˚C with an increase in gadolinium concentration at higher frequencies. The increase in broadness with increase in frequency suggests that the present materials are of ferroelectric relaxor type. The degree of relaxor behaviour (γ)
increases from 1.05 for x = 0.0 to 1.57 for x = 0.8. Hence, the studied relaxor ferroelectrics with diffuse phase transitions (1≤γ≤2) find energy storage applications in different devices such as piezoelectric actuators, multilayer capacitors, medical
imaging devices, non-volatile memories, pyroelectric detectors and microwave tunable applications.