Synthesis And Superconductivity Of Perovskite Barium Bismuth Lead Superconductor

Superconductivity is a well-known macroscopic quantum phenomenon.When a superconductor reaches a superconducting state,it has three characteristics,namely the zero-resistance effect,the Meissner effect and the Josephson effect.According to these characteristics of superconductivity,superconductors have great application in power equipment,computer chips,magnetic levitation trains,nuclear magnetic resonance,long-distance power transmission and other fields,and will bring revolutionary changes to human society.The perovskite-type bismuthate superconductor is a three-dimensional material with isotropic properties and a long coherence length（5-7.5 nm）.Therefore,perovskite-type bismuthate superconducting materials have great potential in applications.In this paper,the optimal doped superconductor BaPb_0.75Bi_0.25O₃ in BaPb_（1-x）Bi_xO₃（0.05<x<0.3）is selected as the matrix,and its A site and B site are doped and modified,as well as its synthesis,structure and superconducting properties are studied.The specific content is as follows:（1）Doping the B site of BaPb_0.75Bi_0.25O₃ with the low-valent element In to obtains the hole-type superconductor Ba(Bi_0.25Pb_0.75)_1-xIn_xO_3-δ（0≤x≤0.14）.Its synthesis temperature ranges from 780℃ to 880℃.Indium doping has little effect on the structure of Ba(Bi_0.25Pb_0.75)_1-xIn_xO_3-δ（0≤x≤0.14）,and all samples have been confirmed to crystallize in the P1 space group.The _CT^zero of Ba(Bi_0.25Pb_0.75)_1-xIn_xO_3-δ（0≤x≤0.14）decreases with the increase of indium in the sample.（2）Doping the B site of BaPb_0.75Bi_0.25O₃ with the low-valent element Mg to obtains the hole-type superconductor Ba(Bi_0.25Pb_0.75)_1-xMg_xO_3-δ.The doping of Mg increases the unit cell volume of the sample.The content of Bi³⁺(Pb²⁺)increases with the increase of Mg.With the increase of Mg in the sample,the_CT^{zer o}of Ba(Bi_0.25Pb_0.75)_1-xMg_xO_3-δ（0≤x≤0.10）gradually decreases.（3）The high-valent element Pr is used to dope the A site of BaPb_0.75Bi_0.25O₃,so that the Ba_1-xPr_xBi_0.25Pb_0.75O_3-δoxide transitions from a hole-doped superconductor to an electron-doped superconductor.All samples crystallized in the P1 space group at room temperature.The unit cell volume of the sample increases with the increase of Pr content,which indicates that some Bi⁵⁺(Pb⁴⁺)is converted to Bi³⁺(Pb²⁺).The change of _CT^{on set}and_CT^zero clearly shows that the Ba_1-xPr_xBi_0.25Pb_0.75O_3-δ（0≤x≤0.07）sample changes from hole-doped to electron-doped.In this paper,the elements In,Mg and Pr are successfully doped into BaPb_0.75Bi_0.25O₃ to form solid solution Ba(Bi_0.25Pb_0.75)_1-xIn_xO_3-δ（0≤x≤0.14）,Ba(Bi_0.25Pb_0.75)_1-xMg_xO_3-δ（0≤x≤0.10）,Ba_1-xPr_xBi_0.25Pb_0.75O_3-δ（0≤x≤0.07）.When the elements In and Mg are doped into the B site,_CT^zero decrease as the doping content increases.When the element Pr is doped into the A site,the sample transitions from hole-doped to electron-doped as the doping content increases.