Polaron assisted hopping mechanism in microwave processed Nd doped second layered aurivillius SrBi₂Nb₂O₉ ceramics

The polycrystalline Sr_0.8Sn_0.2Bi_1.75Nd_0.25Nb₂O₉ (NdSBN) was synthesized using the green synthesis microwave sintering method, which significantly reduced the processing parameters of the NdSBN ceramics. Orthorhombic crystal structure with A2₁am symmetry was revealed by Rietveld refinement study, whereas the doping-induced strain and crystallite size was studied using the Williamson Hall method. Crossectional SEM micrographs confirm the plate-like structure, with an average grain size of 273.7 nm. A diffuse type of phase transition was observed at 345 °C, which usually arises due to compositional fluctuations and mobile oxygen vacancies; further, the diffusiveness of the NdSBN was studied using Uchino and Nomura function, a modified version of Curie-Weiss law (CW). The frequency and temperature-dependent dielectric study of NdSBN ceramics display a Maxwell-Wagner relaxation with a high loss in a low frequency regime, possibly due to the presence of leakage current in the solid solution. Frequency dependent AC conductivity obeys Jonscher's power law, whereas DC conductivity supports polaron assisted hopping in NdSBN composition with dual activation energies of 0.55 eV and 0.75 eV, which correspond to electrons and ions, respectively. The non-Debye type relaxation mechanism in conjunction with negative temperature coefficient of resistance (NTCR) behavior was demonstrated by temperature dependent impedance spectroscopy, while modulus spectroscopy confirmed the multiple relaxation processes in NdSBN ceramics.