Hydrothermal Synthesis And Characterization Of The Double Perovskite-type Manganites

The traditional method of the synthesis of perovskite manganese oxide compounds is high-temperature solid-phase method, although the operation method is simple, easy to master, but the shortcoming of this method is also very typical,for example, the high cost of high-temperature sintering, with intermediate repeatedly grinding, and there are always many vise production as multi-phase or mixed phase. It causes disadvantage for further chemical and physical tests.In this thesis, we mainly discuss the synthetic method and reaction conditions of A, B site doped perovskite type manganese oxide compounds by hydrothermal system, focus on the composition and structure of the product, and part of the series magnetic compounds were characterized. The purpose of this study is to get to the information of the synthesis of ions doped manganite in both A and B site, and achieve the controllability of the composition modulation.1. A Series of compounds with the formula La-Ca-K-Fe-Mn-O has been synthesized under mild hydrothermal conditions, respectively, A site of Ca ions and B-site of Fe ion doping was carried out in detail the composition of the modulation, including the two Part: a)Ca_xLa_yK_1-x-yMnFeO₆(0.1=2+ doped in A site and a detailed study of the compound of preparation conditions, analysis of the product structure, structure and doping effect on the impact of B-bit architecture; b) La_0.5Ca_0.5Mn_1-xFe_xO₃(0.1=3+ doped in B site, introductions of the best synthesis conditions, the product structure was analyzed and gave rise to an analysis of the magnetic changes.Compared with conventional solid-phase synthesis methods, hydrothermal synthesis has a low reaction temperature, the high quality product, uniformed size distribution, regular crystal morphology, etc.. Studies have shown that hydrothermal reaction system conditions require accurate conditions, reactant ratios, crystallization temperature, the alkalinity of reaction system and other conditions were limited to very small changes in range. As the composition of the system complexity, we have adopted a variety of test methods for their valence state, structure and composition. A more detailed analysis and find that the increase in the amount of Ca ion doping on A-site results few changes of the bond length or bond angle of BO₆ octahedron. With the Fe³⁺ doping in B site, changes happen in BO₆ octahedron and with the increasing of Fe³⁺, ferromagnetic of the system weakened while anti-ferromagnetic phase significantly increases.2. A series of double perovskite of B-site Fe, Mn-doped compounds Ln2MnFeO₆ (Ln = Gd, Tb, Dy and Ho) have been synthesized by hydrothermal mothed for the first time. Optimise reaction conditions were reported in this study. The structure and component of this new compound was detected by many instruments. X-ray powder diffraction was used to confirmed its structure by an initial, ICP combination EDS spectra to confirm its composition, further observation of morphology was shown by SEM, the series of work illustrate that the compounds were of high purity, clear crystal structure, and show the advantages of hydrothermal synthesis method one more time. Because few reports about the compound, to make clear the focus on the next stage of the study, we did DSC thermal analysis, found that there is a phase transition about 300℃regularly, whereby we put forward the next stage of the study direction.