Effect of praseodymium on the normal-state and superconducting properties of RBa2Cu3Oy: A comparative study of the role of the Pr ion on R and Ba sites
Ve. Gasumyants et al., Effect of praseodymium on the normal-state and superconducting properties of RBa2Cu3Oy: A comparative study of the role of the Pr ion on R and Ba sites, PHYS REV B, 61(18), 2000, pp. 12404-12411
We present results of a comparative study of the normal-state and supercond
ucting properties in the RBa2Cu3Oy system with substitutions by Pr for the
R and Ba sites. The temperature dependences of the resistivity and thermopo
wer were measured for the SmBa2-xPrxCu3Oy (x = 0.0-0.35) samples and analyz
ed in comparison with data for the Y1-xPrxBa2Cu3Oy system. It was observed
that the Pr-->Ba substitution affects all the properties of the RBa2Cu3Oy s
ystem, both the normal state and superconducting, much stronger compared to
the Pr-->Y one. This manifests itself in an increasing oxygen content, an
orthorhombic-to-tetragonal transition at x = 0.3-0.35, a stronger rise of t
he thermopower value, and a faster T-c drop. The results obtained are analy
zed within a phenomenological narrow-band model in order to reveal both com
mon peculiarities and specific features of the Pr influence on the band spe
ctrum parameters in the normal state when substituting for different lattic
e positions. We have observed that the Pr doping leads to a significant mod
ification of the band spectrum, resulting in a strong band broadening and s
tates localization. At the same time, changes of the total effective width
of the conduction band W-D and the T-c value in two systems with the differ
ent kind of Pr doping are shown to correspond to each other so that the T-c
(W-D) dependence follows the universal correlation for the YBa2Cu3Oy system
with different deviations from stoichiometry. Based on our analysis and in
agreement with earlier suggestions, we conclude that the superconductivity
suppression in both Pr-doped systems could be mainly attributed to the hyb
ridization between 4f states of the Pr ion and the conduction-band states.
In addition, Pr in SmBa2-xPrxCu3Oy on the Ba site acts like other trivalent
rare-earth impurities inducing the extra hole filling effect that leads to
a stronger T-c suppression compared to Y1-xPrxBa2Cu3Oy.