Synthesis And Characterization Of Mixed-valent Manganese Comlpex Oxides

With development of society, synthesis exploring of new materials have become more extensive and important, multi-valent state provide a new degree of freedom to synthesize new materials and bring the exploration of new materials to a more extensive space. RMn2O5-type oxides and perovskite-type oxides AMnO3 are two classical structures which have high tolerance to multi-valence. Furthermore, they are the representative compounds of giant magnetodielectric (CME) materials and giant magnetoresistance (CMR) materials, respectively. In this paper, based on manganese oxides with these two structures, several series of compound were obtained by A or B site doping. Influence of doping ion to the valence state was studied systematically; we also investigated the varied ratio of ions valence influence to the magnetic properties of compounds.In this paper, two series of Fe-doped compounds TbMn2-xFexO5(x=0.1-0.5) and YMn2-xFexO5(x=0.1-0.5) was synthesized by hydrothermal way. The factor of synthesis, such as alkalinity, ratio of start materials have been discussed in detail. As for Tb-system compound, mineralizer impact on the morphology have been investigated, the results imply that cation of mineralizer have important influence to the morphology of compounds. The multi-valence state was studied by XPS. Studies on magnetic properties show that ferromagnetic interaction was enhanced with increased amount of Fe in the system. YMn2-xFexO5(x=0.1-0.5) have also been synthesized to study the magnetic interaction in the Fe-doped system without the interference from magnetic moment of earth ion. The obtained compounds were characterized by XRD, SEM and XPS. Studies on magnetic properties show enhanced magnetic susceptibility and higher Tc temperature in the Fe-doped compounds.A-site doped RMn2O5 compound were also investigated. A series of Tb1-xCaxMn2O5(x=0,0.1,0.2) and Y1-xCaxMn2O5(x=0,0.1,0.2) compounds were obtained under hydrothermal condition, the as-prepared sample were characterized by XRD, SEM. The mixed valance of Mn was determined by XPS, the ratio of Mn4+ is increase along with increasing amount of Ca2+. Magnetic studies on Y1-xCaxMn2O5 (x=0.1,0.2) shows that new Mn4+ introduced by incorporation of Ca2+ bring ferromagnetic interaction to the system by means of Mn3+-O-Mn4+ double exchange. In additional, an unexpected "Curie tail" was observed in the system, caused by unpaired Mn4+ in Mn2O10 bipyramid. We also describe a new route which can systematic synthesis most Zr-doped RMn2O5, in which R is can be rare earth ion from Nd3+to Ho3+and Y3+. In addition, single crystal with bigger size can be obtained by using the new route.Perovskite-type mixed-valence Manganese complex oxides were also investigated in this work. La0.7Sr0.3MnO3 was synthesized by molten salt way in NaCl-KCl system while Ro.5Sro.5Mn03(R=Pr3+, Nd3+) were obtained in NaNO3-KNO3 molten salt system. The obtained samples were characterized by XRD, SEM. Magnetic studies show magnetic properties of Ro.5Sro.5Mn03(R=Pr3+, Nd3+) were quite different from the corresponding bulk materials, reflecting the grain boundary and surface effect influence to magnetic property of nano-materials.