Impact of Mg doping on the structural, morphological and dielectric properties of PbTiO₃ ceramics synthesized by consecutive combination of sol–gel and hydrothermal methods at low temperature

A new hybrid method based on the combination of the sol–gel process and the hydrothermal route was successfully used to prepare Pb_1 − xMg_xTiO₃ (PM_xT) powders with x = 0.0, 0.05, 0.1, 0.2 and 0.3 at low temperature below 200 °C. By modifying the value of x, the impact of the Pb/Mg ratio on the structural, morphological and dielectric characteristics was examined. Analysis of the compounds obtained using X-ray diffraction (XRD) and Rietveld refinement method shows that all the compounds crystallize in a pure perovskite-type phase, demonstrating that magnesium doping within the quadratic structure of PbTiO₃ (P4mm) reduces the tetragonality (c/a) of the crystal lattice, and the proportion of the pseudo-cubic structure (Pm3m) increases progressively, reaching a maximum of 92.38% at a magnesium concentration of x = 0.3. Examination using a scanning electron microscope (SEM) shows that the average grain size decreases as a function of the Mg content, ranging from 4.371 μm for pure PbTiO₃ to 0.412 μm for PT-Mg with x = 0.3. The frequency-dependent dielectric properties were studied by complex impedance spectroscopy in the temperature range from RT to 550 °C where a structural phase transition and two anomalies A and B were observed as a function of temperature at different measurement frequencies for all ceramics, showing a decrease in maximum permittivity (ε_rmax) with magnesium content down to a low value around 30% magnesium (ε = 1248.86), with no significant influence on the ferroelectric-paraelectric transition temperature. The nature of the transition was studied using the Curie-Weiss law, which showed that diffusivity increased with Mg²⁺ ion concentration. This may be explained by compositional fluctuations and structural disorder in the cation arrangement at crystallographic sites.