Mg-induced structural and functional property modulation in Ba1+x/2Ti1−xMgxO3 ceramics for high-frequency capacitor applications

Abstract

Non-stoichiometric barium titanate ceramics with nominal compositions of magnesium-doped BaTiO3 have been synthesized by a conventional solid-state reaction route to study the effect of simultaneous A-site excess and B-site acceptor substitution on the structural, microstructural, optical, ferroelectric, and dielectric properties. Ba1+x/2Ti1−xMgxO3 (BMT) X-ray diffraction combined with Rietveld refinement confirmed the formation of a predominantly perovskite phase, indicating successful incorporation of Mg2+ ions into Ti4+ lattice sites. Increasing Mg concentration induced lattice contraction and decreased tetragonality due to ionic size mismatch and increased lattice distortion. Microstructural studies demonstrated strong grain growth inhibition, defect pinning, and solute drag mechanisms, which reduced the average grain size from ∼ 2.86 μm in pure BaTiO3 to almost 1.00 μm in highly doped compositions. Optical studies revealed a gradual increase in the bandgap to ∼ 3.22 eV, indicating improved optical transparency and suitability for optoelectronic applications. Ferroelectric characterization showed a transition from well-defined ferroelectric hysteresis loops in undoped BaTiO3 to slim relaxor-like polarization loops in Mg-substituted ceramics. Dielectric analysis demonstrated a reduction in dielectric permittivity, a downward shift in Curie temperature, and the emergence of diffuse phase transition behavior, with the BMT3 composition exhibiting a diffuseness parameter (γ) of 3.06. The combined effect of Mg-induced defect chemistry and Ba non-stoichiometry effectively tailors lattice distortion, polarization dynamics, and dielectric stability, making these ceramics promising candidates for high-frequency capacitors and energy-storage applications.