Synthesis And The Study Of Properties On The Iron-based Superconductor Sm_0.95La_0.05O_0.85F_0.15FeAs And PrO_1-XF_XFeAs

Since the discovery of the superconductor F-doped LaFeAsO with Tc=26K at February 2008, and the Tc of some iron-based superconductor even up to 55Kwhich was found a few months later, besides a lot of new superconductors were found. Simultaneously people hope to find the new superconductor with higher TC.In chapter 1, we reviewed the iron-based superconductor's exploration, preparation and design, and also gave the introduction and summary to the mechanism of iron-based superconductor on both theory and experiment aspects. Finally based on the present data, we carried on the comparison at important physical parameters between the iron-based superconductor and the copper oxide superconductor, simultaneously we have foreseen the new superconductor's prospects on application.In chapter 2, we expatiated the fabrication of iron-based superconductor. We succeeded in synthesizing the Sm_0.95La_0.05O_0.85F_0.15FeAs with two-step method. XRD shows the high quality of sample, and the resistivity and magnetic measurement indicate that the onset transition temperature is as high as 57.3 K. We also succeeded in fabricating SmOFeAs with one-step method , and the result and the literature gave basically similar . We also succeed in fabricating Zn-doped sample, and the resistivity measurement indicated that Zn doping restrained the superconductivity.In chapter 3, we studied the raman spectra of polycrystalline SmOFeAs and anisotropic superconducting properties of aligned sample. At first, we studied the raman spectra of undoped SmOFeAs at variety temperature, and observed 6 raman phonon modes. Based on theoretical calculation and other's result, the observed phonon modes were assigned accordingly. Under low temperature, the oxygen Eg mode was suppressed, which was attributed to lattice distortion. Due to the Fe spin-orbital related anisotropic exchange coupling, the tetragonal microcrystalline powder can be aligned at room temperature. A rather small superconducting anisotropy parameterγ 3.0 was observed from anisotropic penetration depth. The linear-T dependence of ab-plane penetration depth ,λab(T) at low temperature suggests the existence of nodes in the superconducting gap.In chapter 4, we studied PrO_1-XF_XFeAs. We succeeded in synthesizing PrO_1-XF_XFeAs(X=0,0.05,0.1,0.12,0.15,0.18,0.2,0.25)series sample. XRD,the resistivity and magnetic measurement indicate the quality of samples. We obtained the F content and Tc phase diagram, which was consistent with other iron-based superconductor.