| The BaPb1-xBixO3(x=0.05-0.35)are superconductors that are substituted for Bi by Pb on the BaBiO3.The superconductors of BaPb1-xBixO3 have good chemi-cal stability without any transition metal elements,and the critical temperature is as high as 13K at optimal doping.In addition,it has a lot of advantages,such as sim-ple structure,isotropic conductivity and superconductivity and long coherence length.Compared with high temperature oxide superconductors,the BiO2 plane is in charge for superconducting.We hope that the superconducting mechanism of high tempera-ture superconductivity will be revealed through the study of superconducting origin in the BaPb1-xBixO3 superconductors.In this thesis,we will discuss the superconduct-ing properties of BaPb0.77Bi0.23O3-? and a serial samples substituted for Ba by Ca or La.In introduction,we briefly introduced the basic properties of superconducting s-tate and the history of superconducting research at first.Then we performed the critical state model,the thermally activated magnetic flux peristaltic model and magnetic flux pinning.Finally,we reviewed the advances of research on superconductivity and dop-ing effect in BaPb0.77Bi0.23O3.In chapter two,we mainly introduced the preparation method of sample and the principle of physical measurement.In chapter three,we introduced the superconductivity of BaPb0.77Bi0.23O3-? which was fabricated by solid-state reaction methods.The experimental results show that the BaPb0.77Bi0.23O3-? polycrystal specimen with zero resistance temperature of 10.4K and the transformation width was 0.2K.The R-T curve of the sample under differ-ent magnetic fields show that the low resistance part of R-T curves conforms to the thermal-activated flux creep model;And the field dependence of effective flux pinning energy shows an exponential behavior,Ueff = U(0)exp(-0.48H).The coherence length is 5.6nm by extrapolation at 0 K.We measured the magnetic hysteresis loop at different temperatures of the sample,and calculated the critical current density and the flux pinning force density of the sample by Bean critical state model.The type of the flux pining in the sample is discussed by the scaling function of the relationship between the pinning force density and the magnetic field.In chapter four,we preformed the effects of Ca substitution Ba on the supercon-ductivity of BaPb0.77Bi0.23O3-?.We prepared the Ba1-yCayPb0.77Bi0.23O3-?(y=0.0,0.025,0.05,0.075,0.1,0.2,0.3)sample by solid-state reaction methods,and measured their XRD and the R-T curves.The results show that Ca substitution Ba has great influ-ence on the critical temperature.When the amount of doping y=0.1,the zero resistance temperature is close to 2K.We measured the R-T curve of the Ba0.975Ca0.025Pb0.77Bi 0.23O3-? and Ba0.925Ca0.075Pb0.77Bi0.23O3-? samples under different magnetic field-s.Two samples show different behaviors in R-T curve under different magnetic fields.The inhibition effect of normal doping on superconductivity is shown in Ba0.975Ca0.025 Pb0.77Bi0.23O3-? samples.But for Ba0.925Ca0.075Pb0.77Bi0.23O3-? samples,inhibition of magnetic field on superconductivity is very severe.The zero resistance temperature is almost inhibited near 2K when the magnetic field is 100G.As the magnetic field increases,the superconductivity disappears.When the magnetic field is higher than 0.2T,the negative magnetoresistance effect occurs in the area below the critical tem-perature.The R-H curve at low temperature shows that the resistance increases with the increase of the magnetic field,and the resistivity of the high-field area decreases with the increase of the magnetic field,and showing negative magnetic resistance behavior.In chapter five,we preformed the influence of La substitution Ba on the supercon-ductivity of BaPbo0.77Bi0.23O3-?.We prepared the Ba1-zLazPb0.77Bi0.23O3-?(z=0,0.1,0.2,0.3,0.4,0.5)sample by solid-state reaction methods,and measured XRD and the R-T curve of the each component.The results show that the effect of La sub-stitution Ba on the critical temperature of BaPb0.77Bi0.23O3-? was relatively slow.The doping amount reaches 0.5,and the zero resistance temperature is 5K when the doping amount reaches 0.5.At the same way,we measured the R-T curve of the Ba0.9La0.1Pb0.77Bi0.23O3-? and Ba0.7La0.3Pb0.77Bi0.23O3-? samples under different magnetic fields,and compared the influence of the doping amount on the H-T relation-ship and the effective pinning energy of the samples.Lastly,we compared the influence of two elements doped on the superconductivity of BaPb0.770.23O3-?.In chapter six,we summarized the full paper. |
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