Structural and dielectric properties of SrBi_2-xPb_xNb₂O_9−x/2(0 ≤ x ≤ 2)

Abstract

Polycrystalline powder samples of SrBi_2-xPb_xNb₂O_9−x/2 (x = 0, 0.25, 0.5, 1, 1.5 and 2) were prepared via the conventional solid state reaction route. X-ray powder diffraction studies carried out on the powdered samples confirmed the possibility of completely replacing Bi³⁺ by Pb²⁺ without altering its basic layered structure. Transmission Electron Microscopy (TEM) associated with Selected Area Electron Diffraction (SAED) studies established the presence of superlattice reflections linked with octahedral tilting. Interestingly, the superlattice reflections in the electron diffraction pattern gradually disappear with increase in lead content in SrBi₂Nb₂O₉. The dielectric properties that were studied in the 100 Hz to 10 MHz and room temperature to 600°C range confirmed the T_c (ferroelectric to paraelectric transition temperature) to be lead content dependent. However, there was no clear well defined ferroelectric to paraelectric transition observed for the compositions corresponding to x ≥ 1. The increase in dielectric constant (ϵ_r) with the increase in lead content at all the frequencies and temperatures under study was attributed to an increase in intrinsic polarization arising from cationic size effect.