Sm_1-xCu_xMnO_3-δ And SrTiO₃-ZrMgMo₃O₁₂ Composites: Synthesis,Thermal Expansion Property And Mechanism

In daily life,what we see is the materials with positive coefficients of thermal expansion（CTE）,but the different of the coefficient of thermal expansion between different materials may lead the materials lose its good performance, such as fracture and failure of the device, and so on. In order to enhance the mechanical properties of component materials, prolong service life, the low thermal expansion materials had been synthesized for its long term prospects and wide application fields. In recent years, many new NTE materials have been gradually synthesized, at the same time, many new theory of NTE materials have also been set up.The ABO3 type perovskite oxide is cubic crystal structure and this optimal structure exhibits numerous physical properties due to the lattice distortions. With the research of the strong coupling between spin lattice, orbital and charge freedom of these materials, a series of physical phenomenon such as colossal magneto resistance（CMR） are gradually discovered and investigated. Additionally, the manganese perovskite oxides like the La1-xAxMnO3 have been applied as the cathode in solid oxide fuel cells（SOFCs） due to their excellent high-temperature stability and thermal expansion compatibility with Yttria Stabilized Zirconia YSZ. Some researchers found the magnetocaloric effect under low field in Ca, Sr doped manganese oxide system. This indicates that the La1-xAxMnO3 also has potential applications in magnetic refrigeration.In the first part of this work, we synthesized a novel Sm_1-xCu_xMnO_3-δmaterial by replacing Cu2+ with Sm3+ in SmMnO3.The preparation, structure, thermal expansion property and negative thermal expansion mechanism was analyzed, the main work and results are as follows:（1） Sm_1-xCu_xMnO_3-δ was synthesized by solid method, it shows the most significant negative thermal expansion when x=0.15, with a thermal expansion coefficient αl=-5.93×10-6 /K（473⁸73K）;（2） Sample Sm0.85Cu0.15MnO3 was mainly composed with homogeneous particles. The diameter of the particles is about 8-9 μm. There are also many pores can be found in the sintered body.（3） Negative thermal expansion phenomenon inSm_1-xCu_xMnO_3-δis due to lattice distortion at room temperature, and the arrangement of cells become much more closer and orderly, accompanied by shrinkage of lattice along one axis direction and the intercellular tiny pore between the cells, material shows negative thermal expansion properties. This NTE property will bring great potential applications to this material in many fields.Another part of this study is the preparation and performance of the composite materialSrTiO₃-ZrMgMo₃O₁₂.ZrMgMo3O12 is a kind of negative expansion properties of negative material, SrTiO3 is an electronic ceramic materials, which has advantages of high dielectric constant and low dielectric loss, it is widely used in electronics, mechanical and ceramic industry. But as a result of high thermal expansion coefficient in SrTiO3, micro cracks appear and lead many physical properties changed, which affects the performance of its combination property. Then we prepared composite materialsSrTiO₃-ZrMgMo₃O₁₂ by solid phase method. We measured the dielectric properties of composite materials through the impedance analyzer, and the linear thermal expansion coefficient of composite materials are measured by thermal expansion instrument. Results are as follows:（1） SrTiO₃-ZrMgMo₃O₁₂ composite was prepared by solid method, with optimum sintering temperature is 600 ℃.No reaction happened and no new substance is generated;（2） SrTiO₃-ZrMgMo₃O₁₂ composite shows low expansion coefficient. Under 100 Hz frequency, composite shows relative dielectric constant at around 2900.