Exploration of the Structural, Dielectric, Ferroelectric, and Piezoelectric Properties in Non-stoichiometric Sr 1−X Bi 2+2X/3 Nb 2 O 9 Ceramics

In this study, the authors focused on the preparation and characterization of Lead-free ferroelectric ceramics known as Sr 1−X Bi 2+2X/3 Nb 2 O 9 : SBBNX, where 0.0≤ × ≤0.4. The ceramics were synthesized using a conventional solid-state reaction route. The researchers performed X-ray diffraction (XRD) analysis to confirm the phase formation and employed the Rietveld refinement technique. The results indicated that the prepared SBBNX ceramics exhibited a single phase with an orthorhombic structure, specifically belonging to the A2 1 am space group. All samples were subjected to analysis using field emission scanning electron microscopy (FESEM) to investigate their surface morphology. The micrographs revealed a uniform distribution of grains (of size 2–4 μ m ) on the surface, with distinct grain boundaries. An increasing trend in both the dielectric constant (from 99 to 220 at room temperature) and transition temperature (from 396 °C to 490 °C) was noted with an increase of Bi content in SBN. The researchers estimated the activation energies by analyzing the Arrhenius plots of the ac conductivity. The obtained values ranged from 0.62 to 1.25 eV, indicating the presence of motion of oxygen vacancies in the SBBNX ceramics. The primary objective of this study was to optimize the Sr/Bi ratio in SBBNX ceramics to enhance their potential use in non-volatile random access memory (NVRAM) applications and high-temperature piezoelectric devices. This study focuses on the impact of substituting smaller Bi 3+ for larger Sr 2+ in SrBi 2 Nb 2 O 9 ceramic. X-ray diffraction (XRD) analysis indicates the successful diffusion of Bi3+ ions at the A-site (Sr2+, ionic radius = 1.44 Å) within the SBN lattice, instead of the B-site (Nb5+, ionic radius = 0.64 Å), resulting in the formation of solid solutions. Field emission scanning electron microscopy (FESEM) images reveal well-defined grains with distinct boundaries. With an increase in Bi substitution, the shape of the grains transforms into elongated plate structures. Notably, the maximum room temperature dielectric constant and piezoelectric constant are observed in Sr 1-X Bi2+ 2X/3 Nb 2 O 9 ceramics, specifically at x = 0.3.