Synthesis of nanosized phases with a garnet structure using supercritical СО2 fluid

Abstract

A method was developed for the production of nanosized complex oxides and oxysulfides. The first stage uses supercritical СО₂ fluid (SAS – supercritical antisolvent method). This approach makes it possible to obtain precursor-free complex oxides in a narrow nanoscale range. Nanosized rare-earth iron garnets with the general formula R₃Fe₅O₁₂, where R is a rare earth element, were obtained and studied by physicochemical methods. The resulting samples have a size of less than 100 nm, exhibit ferromagnetic ordering, and can be used as soft magnetic materials. The multi-stage method for the preparation of complex oxysulfides was not previously demonstrated anywhere in the literature. The method involves three stages. At the first stage, a nanosized X-ray amorphous solid solution of the original salts is obtained using the SAS method. Then a nanosized X-ray amorphous component – the oxide phase – is obtained by annealing in a furnace. After this, the resulting oxide phase is mixed with the disulfide of a transition element (Nb, Mo), and high-temperature annealing is performed in an evacuated quartz ampoule. As a result, compact and nanosized phases of the composition Eu₃Fe_5-3/2xMo_x□_1/2xO_12-2xS_2x and Eu₃Fe_5-3/2xNb_x□_1/2xO_12-2xS_2x, where x = 0.15, were obtained for the first time. The introduction of the sulfide component, namely NbS₂, into the garnet structure increases its magnetic parameters by the factor of 1.5.