The BaFe_12-xGa_xO₁₉ (x < 1.2) hexaferrites were synthesised by usual ceramics technology. The Bi₂O₃ additive in the amount of 3 wt% was applied. The features of crystal structure and unit cell parameters were refined using powder X-ray diffraction at 300 K. It is shown that with the substitution level increase the parameters of unit cell monotonically decrease. The magnetisation and susceptibility versus temperature and field for these solid solutions were investigated by the vibration magnetometry method. The concentration dependence of the main magnetic parameters is constructed. It is shown that with the substitution level increase the magnetic parameters monotonically decrease. The microwave properties of the samples including the external magnetic bias field are also investigated at 300 K. It is shown that with the increase of Ga³⁺ concentration from x = 0.1 to x = 0.6 the frequency value of natural ferromagnetic resonance (NFR) decreases in the beginning, and at further increase in concentration up to x = 1.2 it increases again. With the increase in Ga³⁺ concentration, the line width of the NFR increases that indicates the increase of frequency range where there is an intensive absorption of electromagnetic radiation (EMR). At the same time, the peak amplitude of the resonant curve changes slightly. The frequency shift of NFR in the external magnetic bias field takes place more intensively for the samples with small Ga³⁺ concentration. It is shown the prospects of use of the Ga-substituted barium hexagonal ferrite as the material effectively absorbing the high-frequency EMR.

The possibility of the formation of high entropy single-phase perovskites using solid-state sintering was investigated. The BaO–SrO–CaO–MgO–PbO–TiO₂, BaO–SrO–CaO–MgO–PbO–Fe₂O₃ and Na₂O–K₂O–CaO–La₂O₃–Ce₂O₃–TiO₂ oxide systems were investigated. The optimal synthesis temperature is found between 1150 and 1400 °C, at which the microcrystalline single phase with perovskite structure was produced. The morphology, chemical composition, crystal parameters and dielectric properties were studied and compared with that of pure BaTiO₃. According to the EDX data, the single-phase product has a formula of Na_0.30K_0.07Ca_0.24La_0.18Ce_0.21TiO₃ and a cubic structure.