Influence of Gd Substitution on the Crystal and Defect Structure of BaTi₀.₉₆₅Sn₀.₀₃₅O₃ Ceramics

Abstract

Polycrystalline Ba_1-xGdₓTi_0.965Sn_0.035O₃ (x = 0.00, 0.025, 0.05, 0.075) ceramics were synthesised via a solid-state route to investigate the effect of Gd³⁺ on the structural and microstructural properties of barium tin titanate (BTS). X-ray diffraction (XRD), supported by Rietveld refinement, confirmed a well-crystallised orthorhombic phase (Amm2) with systematic peak shifts indicating successful Gd incorporation. In contrast, a pyrochlore-type Gd₂Ti₂O₇ secondary phase appeared at higher Gd contents (x ≥ 0.05), marking the solubility limit. Williamson–Hall Plots showed that Gd doping reduces lattice strain while preserving long-range crystallinity. Electron-density contour and 3D Fourier maps revealed a periodically ordered lattice with subtle local rearrangements induced by Gd³⁺. FTIR spectra evidenced Ti–O vibrational modes alongside the disappearance of carbonate-related bands. The grain size, as calculated from FESEM micrographs, decreases from 0.721 µm to 0.289 µm due to the solute drag mechanism and the emergence of a secondary phase. Energy-dispersive spectroscopy confirms the elemental makeup of the synthesized samples. Raman spectroscopic analysis agrees well with the XRD studies. These structural and microstructural modifications establish a strong foundation for subsequent investigations into the enhanced dielectric and ferroelectric properties of Gd-modified BTS, highlighting its potential as a lead-free material for advanced capacitors, actuators, sensors, and energy-storage devices.