Structure, electrophysical, optical, and magnetic properties of composites (1-x)PbFe12O19–xPbTiO3

This paper presents the results of studying the structural features and physical properties of two-component composites (1-x)PbFe₁₂O₁₉–xPbTiO₃, obtained from pre-synthesized and mechanically activated powders. To control the physical properties of composites, in addition to changing the dopant (PbTiO₃) concentration within the range of 0.2–0.8 in steps of 0.2, the method of mechanical activation (nanostructuring) was used. This method implies that the Bridgman anvils simultaneously apply a compressive force to the powder placed between them and produce a shear deformation by rotating the lower anvil. X-ray diffraction revealed a sharp decrease in the unit cell parameters of the dopant of the initial composition at x = 0.4, followed by a similarly sharp leap in the parameters of the hexagonal cell after mechanical activation. The dimensions of the coherent scattering regions (D) of the PbFe₁₂O₁₉ component after mechanical activation decreased by more than a half, while the dislocation density (ρ_D) and the magnitude of microstrains (ε) increased by more than an order of magnitude. It was found that the magnetic phase transition temperature of composites decreases by about 14 °C with increasing dopant concentration, and the nanostructuring of composites leads to a further decrease in the transition temperature by another 12–36 °C, depending on the dopant concentration. The band gap E_g of the nanostructured compositions increases by approximately 0.3 eV regardless of the dopant concentration. Using the impedance spectroscopy method, it has been discovered that the dependence of the grain capacitance C_g(T) in the temperature range of 150–350 °C has a bell-shaped form, which is explained in terms of Maxwell–Wagner polarization, where the relaxation is of the non-Debye type.