Magnesium-induced phase transition and enhanced dielectric performance in ((Ba₀.₈₅Sr₀.₁₅)₁₋ₓMgₓTiO₃) ceramics synthesized by the sol-gel method

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A series of Barium Strontium Magnesium Titanate (BST-Mg) ceramics, formulated as ((Ba₀.₈₅Sr₀.₁₅)₁₋ₓMgₓTiO₃) with varying magnesium concentrations (x = 0, 0.88, 0.91, 0.97, and 1.00), were prepared using a sol-gel synthesis approach. To achieve phase stability, the powders were subjected to heat treatment at 950°C for four hours. X-ray diffraction (XRD) analysis, combined with Rietveld refinement performed via FullProf, confirmed that the non-doped composition adopts a tetragonal symmetry within the P4mm space group, whereas increasing Mg content promotes the emergence of a hexagonal structure associated with the R-3 space group. For intermediate compositions, a biphasic region is observed, where both tetragonal and hexagonal phases coexist without any detectable secondary structures. Fourier-transform infrared spectroscopy (FTIR) identified distinct vibrational bands in the 450–600 cm⁻¹ range, characteristic of TiO₆ octahedral stretching and bending modes. Scanning electron microscopy (SEM) analysis revealed greater material densification and finer grain size, with the 0.97 Mg sample exhibiting a highly uniform grain distribution and optimal densification. Based on Williamson-Hall analysis, the estimated crystallite sizes fall within 130–154 nm, with an uncertainty margin of approximately 2–5%. Additionally, dielectric property measurements conducted over a frequency range of 1 kHz to 2 MHz demonstrated a broad phase transition, where dielectric permittivity progressively increases with Mg content while maintaining thermal stability over an extended temperature range. These findings highlight the crucial role of Mg incorporation in tailoring the structural, microstructural, and dielectric attributes of ((Ba₀.₈₅Sr₀.₁₅)₁₋ₓMgₓTiO₃) ceramics, reinforcing their potential application in next-generation microelectronic technologies.