The experimental study of the possibility of synthesis of polysubstituted crystals with the m-type hexaferrites structure in the BaO-Fe2O3-Mn2O3-NiO-TiO2-Al2O3 system

As part of the study of the possibility of structure formation and stabilization in a multicomponent system of high-entropy crystalline solid solutions with the structure of M-type hexaferrites the experimental series with the BaO-Fe2O3-Mn2O3-NiO-TiO2-Al2O3 system were carried out. The system qualitative composition is due to the fact that according to literary data a part of the elements included in its composition increases the hexaferrite crystals anisotropy and increases the ferromagnetic resonance frequency, while others lower it. Consequently, it will be possible to change smoothly the ferromagnetic resonance frequency by adjusting the quantitative material composition and throughput, achieve the values required for this particular application. The charge composition for experimental samples was selected in such a way as to ensure the maximum configurational entropy of mixing. For this aim, the atomic content of Fe, Mn, Ni, Ti, and Al in the expected high-entropy phase with the formula Ba(Fe, Mn, Ni, Ti, Al)12O19 should be equal. In order to obtain Ba(Fe, Mn, Ni, Ti, Al)12O19 crystals, the possibilities were exploited using three different methods for synthesizing experimental samples - solid-phase sintering, melting in a platinum crucible and melting in a stainless steel crucible. According to SEM and EDX results the two main crystals types are hexagonal crystals, which apparently have an M-type hexaferrite structure, and octahedral crystals, which probably have an AB2O4 spinel structure. Based on this, it can be assumed that the formation in this system provides hexagonal polysubstituted crystals (apparently, with the structure of M-type hexaferrites) and the structures stabilization of that provides high values of the configurational mixing entropy of the crystal components.