The Synthesis And Physical Properties Of La_0.67Ca_0.33MnO₃/Sr₂FeMoO₆ Composites And The Structural Stability Of Zn₂SnO₄ Nanowires Under Pressure

Colossal magnetoresistance (CMR)-a huge decrease in resistance in response to a magnetic field-has recently been observed in materials with perovskite structure and ordered double perovskite structure. This effect gives rise to considerable interests from both fundamental and practical points of view. Sr2FeMoO6 with ordered double perovskite structure exhibits intrinsic tunnelling-type magnetoresistance at room temperature. Its fairly high magnetic transition temperature (Tc) is about 420 K. La0.67Ca0.33MnO3 with a perovskite structure has CMR effect around Tc (the maximum Tc is about 250 K). Its CMR effect can be explained by the Zener's Double Exchange mechanism. In order to get novel materials having CMR effect, we prepared for the series of composites of Lao.67Cao.33Mn03 and Sr2FeMoO6, which have sizes below 50 nm, using polymer-network sol-gel technique.We performed x-ray diffraction experiments and scanning electron microscope (SEM) observations. Through x-ray diffraction, we have characterized the structures of the composites. We find from SEM observations that the composites have compacted connection among grains. High resolution transmission electron microscopy and in situ SEM energy dispersive x-ray analysis was also been carried out. All the results we obtained prove the feasibility of the complex route. The measurements for magnetic and electrical properties were also taken.Optically transparent and electrically conducting oxides (TCO) have attracted many scientists due to their unique optical and electronic properties and widespread and successful applications in recent years, such as smart windows, thin-film photovoltaic, flat-panel displays, polymer-based electronics and architectural windows.The purity of the synthesized Zn2Sn04 (ZTO) nanowires was checked by XRD and all the sharp diffraction peaks can be indexed to a fcc inverse spinel structure with a space group of Fd3m and lattice parameter of a=8.61±0.01 A. We utilized in situ high-pressure ADXD experiments and in situ high-pressure Raman scattering investigation to study the phase transition of ZTO nanowires under high pressure. With increasing pressure, an intermediate phase with an orthorhombic structure appears at 15.5 GPa and a high-pressure phase occurs at about 32.8 GPa. The high-pressure phase of ZTO is considered to possess the ambient pressure structure of CaFe2O4.