Non-debye type conduction mechanism in Gd doped SrBi₂Nb₂O₉ ceramic prepared through single-step microwave sintering method

Lead-free polycrystalline SrBi_1.75Gd_0.25Nb₂O₉ (GdSBN) ferroelectric ceramics were prepared through a conventional solid-state reaction route by incorporating novel microwave sintering (MS) technique which effectively reduces the two-step sintering process to single step sintering. A single-phase orthorhombic crystal structure (A2₁am) without any sort of impurities or fluorite phase was revealed from X-ray diffraction. The doping-induced strain was further studied using the Williamson–Hall (W-H) method, which comes around 1.3x10^-3. The cross-sectional SEM micrograph confirmed the Aurivillius structure of the composition with an average crystallite size of 1.2 µm. The frequency (20 Hz–1 MHz) and temperature (25 °C–550 °C) dependent dielectric study of microwave sintered GdSBN displays a relative permittivity of the order of 10³ at high temperatures and obeys Maxwell-Wagner relaxation. Additionally, a low dielectric loss of around 30 was observed from the dielectric spectroscopy. Dielectric characteristics further follow the diffused ferroelectric to paraelectric phase transition at 395 °C, which indicates the presence of space charge polarization in the system. The room temperature P-E hysteresis loop specifies the presence of ferroelectric properties in GdSBN, with remnant polarization (2P_r) of 0.04 µC/cm². Impedance and modulus spectroscopy reveal the non-Debye type relaxation and negative temperature coefficient resistance (NTCR) behavior of the material that is associated with the multiple relaxation processes. Temperature-dependent AC conductivity indicates an Arrhenius-type electrical conductivity of the order 10^-7 S/cm and perfectly obeys Jonscher's formulation. The obtained results indicate that GdSBN Aurivillius composition can be used as a potential candidate for high-temperature piezoelectric sensors.