| The new superconductor of MgB2, with critical temperature of about 39 K, attracts much attention in condensed matter physics, chemistry and material science fields, and so on. On the theoretical side, the study of MgB2 is very useful and important for understanding the mechanism of superconductivity and exploring new superconductor with higher . In the application research field, it is also worth to investigate the superconductor of MgB2. This is not only because of the simpler structure of the sample, lower cost of raw materials of both Mg and B, but also of the excellent properties, such as higher critical current density, higher upper critical field, et al. All of these indicate that the superconductor of MgB2 is a good candidate for many applications. There are many ways to synthesize the superconductor of MgB2. However, the processes of these ways are very complex. In this thesis, we introduce a new method to prepare the superconductor of MgB2, called " press-bury method " (PBM). This new method is easy and convenient to use in lab. The details of PBM are as follows:Firstly, the metal of Mg is cleaned and cut in small granules with a size of 1 mm3. Then, a stoichiometric mixture of Mg and B are pressed into pellets, After buried in Al2O3 powder inside a Al2O3 crucible, the pellets are sintered together with the container in a tube furnace. Finally, the samples are obtained when the furnace is cooled to room temperature. The critical temperature of the sample by this method is as high as 38.8 K, similar to those prepared by the conventional ways. The conditions for preparation of MgB2 samples by PBM are investigated. The experimental results indicate the sintering temperature and soaking time affect the critical temperature greatly. The samples sintered between 800 oC and 850 oC in half an hour exhibit higher critical temperature. At 850 oC, the critical temperature of sample decreases with the increase of soaking time. So we choose the sintering temperature is between 800 oC and 850 oC, the soaking time is in half anhour. Under this condition, the quality of the superconductor of MgB2 can be improved.The impurities strongly affect on the superconductivity of MgB2. The critical temperature as well as the residual resistance ratio () is determined by the temperature dependence of the resistance measured under four-probe method. The decrease of both and mean of a high density of impurities in the samples. The relationship between and is explored in a group of MgB2 samples sintered at 850 oC in 0.5, 1.0, 1.5, 2.0, and 3.0 h, respectively. We find that and decrease as the value of increases. This is different from the common opinion: higher the , higher the . We believe that the contribution to resistance from the impurities will conceal that from MgB2 phase if the impure content is sufficient. More impurities cause the deterioration of , since longer sintering process is beneficial for the formation of impurity.The superconductors of Mg1-xInxB2 ( = 0, 0.01, 0.02 and 0.03 ) are studied. The relationship of the samples are measured. From the relationship we can see that the critical temperatures of Mg1-xInxB2 ( = 0, 0.01, 0.02 and 0.03 ) decrease as In-content increase. In addition, the diffraction spectrum shows that both 002 peaks and 110 peaks shift to smaller angles as In-content increase within a range of from 0.01 to 0.03. Hence, we believe that In substitutes Mg in MgB2 samples which makes the number of holes decrease and results in the decrease of the critical temperatures.For investigating the substitution effect on the magnetic properties, the upper critical lines ( - ) are constructed by the measurement of under various magnetic fields. The curve of vs. exhibits a linear behavior. Thus a formula of is used for linear fitting of with respect to . We find that the lines of upper critical field obtained from different samplesexhibit an interesting trend: the higher the In-content in Mg1-xInxB2 ( = 0, 0.01, 0.02 and 0.03 ) samples is, the steeper the l...
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