The relation of real structure to the electric and magnetic properties of superconducting ceramics remains in the center of interest for several years ([1],[2]). Our study was performed on two sets of samples A and B with the nominal composition $Bi_{1-x}Pb_{x}Sr_{0.8}Ca_{1}Cu_{1.4}O_{y}$,\, (x=0.15, 0.20, 0.25, 0.30, 0.40) prepared by mixing, pelletizing, grinding and heating processes. The samples A were slowly cooled after the last annealing step, whereas the samples B were quenched in liquid nitrogen.
The microstructure parameters were studied by x-ray powder diffraction technique with Bragg-Brentano focusation. Intensity data were collected over $2 \theta $ ranges 4$^{o}-8.5^{o}, 15^{o}-80^{o}$ and analyzed both by Rietveld refinement and Difpatan program in order to get lattice parameters, fractional coordinates of atoms and precise phase analysis of all 10 specimens. The dominant concentration of high-$T_{c}$ phase $(BiPb)_{2}Sr_{2}Ca_{2}Cu_{3}O_{y}$ ($T_{c}\doteq 110K$)was found in all samples excluding Pb concentration $x=0.40$ set B,(Fig.1).
The quality of superconducting transitions were characterized by four probe electrical resistivity measurements in the temperature range $30K-300K$. Every curve defined the value of $T_{c}$ and width of superconducting transition $\Delta T_{c}$. The dependence of $T_{c}$ for both sets of samples on Pb concentration is shown in Fig.2.
A decrease of mass fraction $w$ of the high-$T_{c}$ phase with increasing concentration $x$ of Pb-atoms was found in both sets of samples. No influence of phase composition changes on $T_{c}$ and $\Delta T_{c}$ for samples of A-set was observed. For all quenched samples (set B) strong decrease of $T_{c}$ and elevation of $\Delta T_{c}$ was found. Changes of lattice parameters and the distance changes between atomic planes for slowly and rapidly cooled samples indicate a structural distortion caused by oxygen deficiency in quenched samples.
1. Jinhua Ye et al.:Phys.Rew.B, 48 (1993) 7554
2. Akihiko Nishida et al.:Jpn.J.Appl.Phys.,33 (1994) 4583