【作者】 祝琳琳；

【导师】 冯守华；

【作者基本信息】 吉林大学 ， 无机化学， 2009， 博士

【摘要】 本论文致力于由简单锰氧化物到复合锰氧化物的水热合成研究以及对产物的性质探索,研究主要集中于讨论合成条件对于产物的影响,并在深入了解这些因素的基础之上找到了一些水热合成新材料的有效方法进而对其产物的磁电性能进行部分研究。在第一章绪论中,系统的介绍了有关锰氧化物的关于磁电方面的一些相关基础知识,并对钙钛矿锰复合氧化物的最新研究进展进行了总结;在第二章中,介绍了水热条件下对7个稀土锰氧化物单晶进行了合成,其中三个为正交介稳相,4个为六方相;在第三章中分别介绍了K离子掺杂和Ca、K离子共掺杂的La1-xKxMnO3和Pr0.71Ca0.19K0.1MnO3的单晶样品的合成手段、形貌、结构以及电学性质表征。本论文详细阐述了上述化合物的合成条件和方法、结构特点及性质,并仔细考察了影响各种产物水热稳定性的因素并对其性质进行了部分探讨,为进一步研究新材料的合成与性质探索奠定了基础。更多还原

【Abstract】 The manganese perovskites exhibit magnetic, orbital, and charge orderings caused colossal magnetoresistance (CMR), multiferroics, and superconducting. The manganese perovskites RMnO3 in which R is a trivalent rare earth ion .When it comes to the heavy rare earth atoms such as Ho-Lu, Y and Sc, RMnO3 usually exists in the form of a metastable and non-centrosymmetric hexagonal structure (space group P63cm), and when it is the light rare earth atoms from La to Dy, one can get it in the orthorhombic structure (space group Pbnm) .Both the hexagonal and the orthorhombic structures are derived from distorted cubic perovskite structure. The hexagonal phase usually shows ferroelectromagnetic behavior which possesses both magnetic and ferroelectric orderings, whereas the orthorhombic phase exhibits incommensurate antiferromagnetic structure at low temperature.The synthesis for perovskite manganites could be carried out in many ways, and conventionally used ones were the solid-state reaction, sol-gel method, and co-precipitation. However, these methods need high temperatures. A method with the advantages of lower temperature, easy handling and one-step synthesis was employed to prepare manganites in hydrothermal system. As we know that, the formation of hexagonal RMnO3 strongly competes with the orthorhombic phase in those conventional synthesis methods. For example, the orthorhombic manganites RMnO3 (R=Ho-Lu) synthesized by solid-state reactions at 1573K and 6GPa in a belt-type press must be rapidly cooled down to room temperature to protect the phase transition. By the citrate method, HoMnO3 and YMnO3 were prepared as hexagonal phase We have reported previously the synthesis for the pure orthorhombic phases of RMnO3 (R=Sm-Ho) by hydrothermal method at relative lower temperature compared to other methods. Here we report that the stable orthorhombic phase and the metastable hexagonal phase of RMnO3 (R=Er, Tm) were prepared selectively under hydrothermal conditions at relative low temperature and so many influencing factors for hydrothermal conditions were discussed. Using these new synthesis methods, four new products were prepared and most of them were potassium-doped manganates.Hexagonal and orthorhombic perovskite RMnO3 (R=Er, Tm) were selectively prepared by hydrothermal method, using Mn2O3 andγ-MnO2 as precursor, respectively. Pure phase of hexagonal and orthorhombic RMnO3 (R=Er, Tm) were respectively synthesized by selecting different reaction temperatures and alkaline hydroxides. Powder XRD data of hexagonal and orthorhombic RMnO3 (R=Er, Tm) were refined and SEM photographs show that their homogenous crystal size ranged from 20 to 25 um. DC susceptibility measurements indicated their antiferromagnetic ordering at low temperatures.The potassium-doped manganates, La0.69K0.31MnO3、La0.69K0.31MnO3、La0.80K0.20MnO3 and Pr0.71Ca0.19K0.1MnO3 were synthesized under hydrothermal conditions for the first time.The crystal was synthesized by the so-called hydrothermal reaction of MnO2 under the condition of strong alkali media. The study indicate that formation of the material is dependent on the different precursors and reaction temperature. SEM photographs show that their homogenous crystal size ranged from 15 to 20 um .更多还原