Effect Of Pr And Se Doping And Its Physical Properties In SrFBiS₂ System

Superconducting materials with layered structure,such as Cuprates and iron-based superconductors,have always attracted scientists’attention and research interests.In 2012,the discovery of BiS₂-based superconductor Bi₄O₄S₃ has attracted great interest from scientists,and a serie of BiS₂-based superconductors Ln（O,F）BiS₂（Ln=La,Ce,Nd,Pr）with tetragonal structure have been found and investigated.The study in this dissertation focuses on two important contents:Firstly,investigating the superconductivity,electronic phase diagram and pressure effect in Sr_1-xPr_xFBiS₂;secondly,discovering the double doping effect of Pr and Se and superconductivity in Sr_0.5Pr_0.5FBiS_2-xSe_x.In Sr_1-x-x Pr_xFBiS₂ system,we report the superconductivity of Pr doping samples at atmospheric pressure and the optimal-doping sample’s pressure effect by the electrical and magnetic transport measurements.As 0.4≤x≤0.7,the samples exhibit superconductivity and the maximum value of T_c is 2.7 K at x=0.5.We also perform the external pressure on the optimal doped Sr_0.5Pr_0.5FBiS₂sample and investigate its superconductivity.Pressure can enhance the T_c sharply from 2.7 K to 9.7 K at about 2.5 GPa.According to our research results,the superconducting electronic phase diagram of pressure-temperature was established.In this part,we have studied the double doping effect of Sr_0.5Pr_0.5FBiS_2-xSe_x（0.2≤x≤1.2）system.the superconducting T_c increases slowly with the increase of Se doping content from 2.7 K to 3.5 K（60%Se contents）.The measurements of magnetic susceptibility display,As x>0.5,the superconducting volume fraction increases with the increase of Se doping content and reaches its maximum value of90%,conforming the bulk superconductors.