Electronic properties of the layered compounds with the general composition Ban+1(Pb,Bi)nO3n+1 are quite interesting as the crystal structure of these materials is quite similar to that of high-Tc cuprates. We have investigated the effect of Bi and In substitution on the structure, oxygen stoichiometry (carrier concentration) and the electronic properties of Ba4Pb3O10 compounds. The X-ray powder diffraction results indicate that the unit cell symmetry changes from body-centered tetragonal to cubic with the increasing concentration (x) of Bi and In. The oxygen stoichiometry of the materials is found to increase monotonically with the increase in x(Bi). On the other hand it decreased almost linearly with the increasing x(In). Resistivity of the materials is measured as a function of temperature in the temperature region 3-300K. It is found that the room temeprature resistivity increases with increasing x(Bi/In). Since the oxygen stoichiometry values suggest an increase in the carrier concentration with increasing x(Bi/In), it appears that the disorder caused by the substitution at the Pb site has lead to the carrier localization. For x(Bi)<0.2, we found that the resistivity varies as a function of lnT, which is indicative of weak localization. However, at higher concentrations 3D-VRH behavior is observed. On the other hand the resistivity of indium substituted samples show M-I transition, at low concentrations.
Electron probe microanalysis (EPMA) is being utilized to characterize the composition of superconductors in the Bi-Sr-Ca-Cu-O system (BSCCO) that are doped with minor amounts of transition metal
s. Specifically, the Fe Group (Fe, Ru, Os), the Co Group (Co, Rh, Ir), the Ni Group (Ni, Pd, Pt), the Zn Group (Zn, Cd, Hg), and the other elements in the Cu Group (Ag, Au) can be used as dopants. These first long period ions in their common valence states have similar ionic radii, so only small lattice distortions are expected when other first period ions are substituted for Cu. Our research involves the systematic study of the effect of transition metal substitutions (for Cu) on the properties of the two high temperature superconductors, Bi2Sr2CaCu2O8+δ (2212) and Bi2Sr2Ca2Cu3O10+δ (2223).Substitution for Cu with transition metal ions enables one to see what effect the changing d and s character of the ions have on the superconducting properties of these compounds.
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