| Manganese perovskites provide an ideal natural laboratory for studying the physics of strongly correlated electronic systems, since many basic interactions to exist and the interactions can be varied at will. A detailed study of these materials has been one of the frontiers in condensed-matter physics and material science due to potential application of colossal magnetoresistance (CMR) found in these oxides.In this dissertation, we use the optimal hole-doping manganites as the matrix material for our study and prepare the composites by mixed it with some oxides. The transport properties of the composites are studied under a zero and applied field.In chapter one, the study and progress of manganese perocskites and the research destination of my thesis have been briefly summarized.In chapter two, we describe the study of CBN and the latest progress in this field. In chapter three, we describe the preparation methods of the samples, for example, solid-state reaction, mechanical alloy and the composite method of samples. We discuss detailedy the influences of the different preparation technology on the samples. We intend to find the best process of the samples preparation.In chapter four, we investigate the phase structure and electronic structure in our CBN samples.In chapter five, we investigate the effect of BN doping on the structure and electronic and magnetotransport properties of La0.7Ca0.3MnO3/BN composites. We observed that that all the samples are fine compositions. The BN mainly goes into the grain boundary region of LCMO. When BN doping level are at the range of 0-20%, the metal–insulator transition temperature (TP) does not change (nearly at 263k) and then the resistivity increases sharply with the increase of the BN doping level. At high doping level (x>0.20), Tp decreases greatly, and the resistitvity increases sharply.
|
PDF Full Text Request