| When man came into informational era, great changes have taken place in advanced materials, which quickly renewed the hardware of computer. For examples, high speed hard-disc and CPU. As well known, hard-disc is relative to magnetic materials, and CPU device be consisted of MOS transistors and capacitors which are related to dielectric materials, therefore, new materials such as colossal magneto-resistance materials and high permittivity dielectric materials have been extensively studied in the past several years. For magnetic materials, since in 1993 colossal magnetoresistance (CMR) effect was found in La2/3Ba1/3MnO3 perovskite, great attention has been paid to this field. Though their prospects in application are very bright, the structures and properties of these complex oxides have not been very clear and many problems need to be resolved prior to application. The first part in this thesis will discuss the complex structure and the thin films of these metal oxides. For the high permittivity dielectric materials, we know, the design of conventional dynamic random access memory (DRAM) uses the amorphous SiO2 on the surface of Si substrate, a simple and ripe procedure. However, to accommodate the change of the market, the density of DRAM needs higher and higher. And this requires a decrease of thickness of amorphous SiO2 layer. However, scaling to some extent, the device can not be used because of the large tunneling current. Then, one of the best methods is to replace the low constant dielectric SiO2 by high permittivity materials. Its merit is that we can continue to use old procedure. However, many problems also need to be resolved, such .as thermodynamic stability, interfacial quality, leakage current and so on, these complications are making devices more complex and expensive. Under this circumstance, many researchers are trying their best to look for the high permittivity materials satisfying the above two requirements.In this thesis, we have investigated the magnetic materials and dielectric materials in different topics. The results are presented in the followings.1. Orthorhombic to Cubic Phase Transition in La1-xCaxMnO3 PerovskitesIt is very interesting in exotic oxides La1-xCaxMnO3, when x<0.5, colossal magnetoresistance (CMR) effect can be observed, however, when x>0.5 and the temperature is decreased to lower than Tc, charge-, orbital-, and spin-ordering and correlated properties may appear. Chen et al. believed the twin-related domains in charge-ordered La1/3Ca2/3MnO3 were charge-ordered domains. Wang et al. systematically studied orientation domains in La1/3Ca2/3MnO3 perovskite by transmission electron microscopy, and observed them even at room temperature (RT), when charge-ordering did not take place. By group-theoretical analysis they concludedthat these orientation domains were induced by a displacive phase transition from cubic to orthorhombic perovskite at higher temperature.Here the variations of the polycrystalline X-ray diffraction patterns of La1-xCaxMnO3 perovskites (x=3/8, 1/2, 2/3) with composition and temperature have been studied. When temperature increased to 750癈 or 900癈, a phase transition from orthorhombic to cubic perovskites was observed for the first time. This phase transition confirms further that the orientation domains in the La1/3Ca2/3MnO3 are induced by cubic to orthorhombic phase transition, but not by charge-ordering. Moreover, the unit cell parameters ao, bo and Co of these orthorhombic perovskites at room temperature, and also ap of these cubic perovskites at high temperature, decrease with increasing x.2. Microstructures of epitaxial La0.7Ca0.3Mn0.3 thin films grown on SrTiO3 and NdGaO3 substratesPerovskite La0.7Ca0.3MnO3 thin films were epitaxially grown on SrTiO3 and NdGaO3 substrates by pulsed laser deposition. The microstructure of these films was investigated by means of transmission electron microscopy. Due to the small lattice mismatch in the system of LCMO/NGO, the films showed a higher structural perfection than the films on...
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