多铁性材料由于兼具铁电性与铁磁性，并且不同的铁性间可相互耦合产生新性能，为发展新型器件模型提供了广阔的应用前景。本论文以制备多铁性铁氧体/钙钛矿结构铁电氧化物的核/壳(core/shell)纳米结构为主要研究内容，提出了水热和热处理相结合的两步法制备core/shell结构的基本思路，并研究了各种形貌的铁氧体和钙钛矿结构氧化物纳米颗粒的合成方法。利用水热法，在乙二醇-NaOH体系中合成了Fe3O4，CoFe2O4，NiFe2O4，和MnFe2O4 等球状铁氧体颗粒。通过调节反应物配比，制备了形貌和磁性能可调的Fe3O4颗粒。将水引入反应体系，通过调节实验参数，制备了一系列不同物相组成，形貌，颗粒尺寸以及磁性能的铁的氧化物纳米颗粒。在所有的Fe3O4形貌中，链状结构尤其特殊，其组成单元具有显著的自组装特征。该链状结构在室温下饱和磁化强度高达90 emu/g，第一磁晶各向异性常数大小为6.03×105 erg/cm3，远高于块体材料。该合成方法还可以推广合成诸如掺杂的Fe3O4链，Co链等其他的自组装磁性链状结构。在含有KOH的乙二醇体系中，制备了花状K2Ti6O13颗粒。该花状结构是由一维的纳米结构自组装而成的，其典型的形貌有荷花状，菊花状，蒲公英状等。如果将碱变为Ba(OH)2，产物经过水热和热处理后可以得到结晶良好的花状BaTiO3颗粒。在这个思路的启发下，制备了BaTiO3，PbTiO3 , SrTiO3 和Pb(Zr,Ti)O3等单分散的球状钙钛矿结构氧化物颗粒。利用水热和热处理结合的方法实现了ABO3结构钙钛矿壳层的理想包覆，先通过B位离子的水解使其包覆于铁氧体颗粒之上，经过后续的水热反应和热处理过程，使A位离子与B位离子原位反应结晶。制备了Fe3O4/PbTiO3, γ-Fe2O3/PbTiO3, γ-Fe2O3/Pb(Zr,Ti)O3, CoFe2O4/BaTiO3, CoFe2O4/PbTiO3以及CoFe2O4/Pb(Zr,Ti)O3等一系列core/shell纳米复合颗粒。包覆后的两相表现出强的相互作用，铁电层的存在极大的影响了复合体系的晶体结构，电阻率，介电损耗，磁性能以及居里温度等重要参数。在γ-Fe2O3/Pb(Zr,Ti)O3体系中，当热处理温度为750 °C时，铁氧体核心转变为PbFe12O19，从γ-Fe2O3/PZT到PbFe12O19/PZT，复合体系的矫顽力从69.3 Oe 变为 2552.7 Oe。

Multiferroic materials with coexistence of ferroelectricity and ferromagnetism have recently attracted increasing interest because of their significant technological promise in novel multifunctional devices. In this thesis, we report a general approach for the fabrication of ferrite/perovskite oxide core/shell nanostructures with uniform size and shape by a combined hydrothermal and annealing process. In the process of exploring the ideal coating method, the research work also focuses on the synthesis of spherical shaped ferrites and perovskite oxides particles.Monodisperse spinel ferrite microspheres crystals, including Fe3O4, CoFe2O4, NiFe2O4, and MnFe2O4, have been synthesized by a simple hydrothermal method. In the synthesis of Fe3O4, by adjusting the initial molar ratio of NaOH to Fe3+, several morphologies can be obtained. The magnetic properties of the as-synthesized samples show an evident variation trend as the morphology and grain size change. In the ethylene glycol (EG)-water-NaOH system, by adjusting the experimental parameters, the shape, size, phase and magnetic property of the products can be easily controlled. In all the Fe3O4 morphologies, the spherical chains building up by tens of self-assembled microspheres are even special. The chain-like structure shows very high saturation magnetization value of 90 emu/g at 300 K. Magnetization-temperature measurements reveals very strong interparticle interactions in the assemblies, and the first-order magnetocrystalline anisotropy value of 6.03×105 erg/cm3 is obtained. Further experiments indicate that the present hydrothermal method in the EG-NaOH system is well applied to synthesize other kind chain-like materials such as doped Fe3O4 chains and Co chains.In the EG-KOH system, flower-like K2Ti6O13 nanostructure is synthesized via a hydrothermal method. Results show that the flower-like K2Ti6O13 particles were assembled by one-dimensional nanostructures and several typical morphologies are obtained. If the reaction is conducted in the Ba(OH)2 solution, after hydrothermal and annealing process, flower-like BaTiO3 can be obtained. Based on the results above, monodisperse spherical-shaped BaTiO3，PbTiO3 , SrTiO3 and Pb(Zr,Ti)O3 particles with adjustable sizes and narrow size distribution are obtained.A general combined hydrothermal and annealing process for the fabrication of ferrite/perovskite oxide core/shell nanostructures is introduced. The coating of a perovskite oxide (ABO3) layer on spherical ferrite particles is performed in two steps. A dense and smooth amorphous layer containing B-site ions of the perovskite oxide is coated first via a controlled hydrolysis and aging process. During hydrothermal treatment and subsequent annealing process, the A-site ions are incorporated in situ into the as-coated amorphous layer preserving the spherical morphology. This synthesis of ferrite/perovskite oxide core/shell nanostructures are demonstrated in systems like Fe3O4/PbTiO3, γ-Fe2O3/PbTiO3, γ-Fe2O3/Pb(Zr,Ti)O3, CoFe2O4/BaTiO3, CoFe2O4/PbTiO3 and CoFe2O4/Pb(Zr,Ti)O3. This method allows the shell thickness of the composite particles to be manipulated in a controlled manner with various core sizes. After coating, the core and shell materials show strong interactions. For the γ-Fe2O3/Pb(Zr,Ti)O3 core/shell structures, the PbFe12O19 phase is formed when the nanoparticles are annealed at 750 °C. These core/shell nanostructures show well-defined interface and highly oriented growth. From γ-Fe2O3/PZT to PbFe12O19/PZT, the coercivity changes from 69.3 Oe to 2552.7 Oe.