Publication
Journal of The Less-Common Metals
Paper

123 Near equilibrium samples: Anomalies of the lattice parameters and some physical properties

View publication

Abstract

Contrary to the literature, the dependence on nonstoichiometry of the lattice parameters of "nearly" equilibrated 123 samples (particularly the c- and b-axis), shows strong changes of slope in the nonstoichiometric range x = 6.8-6.9. At x = 7.0-6.9 the c-axis decreases with decreasing oxygen concentration. And at x ≅ 6.9 the well known trend sets on:increase of c-axis and decrease of b-axis with decreasing oxygen content. These changes are reflected in the physical properties investigated up to now: &#x02022; The dependence of Tc on hydrostatic pressure is < 0.05 K/kbar for x > 6.9, increases strongly in the range x = 6.9-6.8 and shows a change of slope at x = 6.8 where it has reached the value dTc/dP = 0.35 K/kbar. At x = 6.5 is dTc/dP = 0.45 K/kbar. (Also the tc as a function of nonstoichiometry shows the well known decrease at x = 6.8). &#x02022; The muon spin-depolarization rate as a function of nonstoichiometry shows also an unexpected strong decrease (25%) in the range x = 7.0-6.9. This suggests that the density of the superconducting carriers decreases strongly in this range. It seems possible from the lattice parameter effects that a threshold concentration of oxygen vacancies in the chains is necessary in order that the expansion of the apical bond sets on. © 1990.