Substitution-induced near phase transition with Maxwell-Wagner polarization in SrBi2(Nb1-xAx)2O9 ceramics [A=W, Mo and x=0, 0.025]

The synthesis, micro-structure, spectroscopic, and dielectric properties of SrBi2(Nb1-xAx)2O9 [with A=W, Mo and x=0, 0.025] ceramics were systematically studied. A relative density of 98% was obtained for all the samples using a two-step solid state sintering process. XRD images showed that a single phase layered perovskite structure of SrBi2Nb2O9 (SBN) was formed. The orthorhombic structure with A21am phase group was found up to approximate to 2.5at.% substitution of W and Mo into the SBN matrix. SEM revealed the rod-like grain structure similar to the Maxwell-Wagner (MW) parallel plate capacitor model in SBN ceramic, whereas smaller heterogeneous grain structure was observed in W and Mo donor doped ceramics. The initial high value of real and imaginary part of relative permittivity also indicated the presence of interfacial MW relaxation in the SBN ceramics. The experimental data fit well to the theoretical data obtained from MW polarization model in SBN ceramics. The possible origin of the difference of the properties present in the doped sample has been explained based on grain size, orientation, and modification done in the ceramic matrices.