A comparative study of Pr substitution at Y and Ba sites in YBa2Cu3O7
Abstract
Aimed at identifying the factors which suppress the superconductivity in cuprate perovskites I have
investigated the effect of substituting Pr ions at the Y and Ba sites in YBa 2 Cu 3 O 7-d system using structural,
transport, iodometric, and photoemission studies. The rate of Tc depression in the case when Pr substitutes
the Ba site is much higher than the case when it substitutes the Y. This is explained as being due to a combined
effect of the factors such as depletion of itinerant holes due to depletion of the oxygen content, the Pr 4f - O 2p
hybridization, shortening of c-axis causing Cooper pair-breaking, and the loss of orthorhombicity.
Introduction
The mystery of evolution of superconductivity in cuprates remains
illusive past more than two decades of its discovery [1–4].
Identification of the factors which suppress superconductivity in
them must be explored in order to unravel the mechanism of
superconductivity [4,5]. The Pr substitution in YBCO-123 system
continues to hold the interest of researchers in this regard [5–9]. Most
of the studies have been carried out substituting Pr at Y site. Many of
these have, however, reported some Pr ions occupying the Ba site
even though the entire Pr substitution was intended for the Y [6–8].
The Pr ions at the Ba site are ascribed to play significant role in
quenching of superconductivity [5–7]. The tendency of Pr 3+ ions
(ionic radii 1.013 Å) to occupy the Ba 2+ site (1.34 Å) is ascribed to the
closer values of the ionic radii of the two compared to that of the Y 3+
(0.893 Å). Thus, Pr 3+ has a substantial solubility (~15%) at the Ba site
[10]. In this work, I have intentionally substituted the Pr at Ba site to
compare the outcome with the case when the Pr is substituted at Y,
with regard to quenching of superconductivity. Besides a careful
characterization, the powerful X-ray photoemission spectroscopy
(XPS) [4,5] was employed to explore the electronic structure.
Conclusion
I studied YBa 2 Cu 3 O 7 − δ with Pr substituting both the Y and the Ba
sites. The rate of Tc depression, in the case when Pr substitutes the Ba,
is much higher than the case when it is substituted at the Y. This is
explained as being due to a composite effect of the depletion of
itinerant holes due to depletion of the oxygen content, the Pr 4f–O 2p
hybridization, shortening of c-axis causing Cooper pair-breaking, and
the loss of orthorhombicity. Further studies are required to pinpoint
which of these factors is more prevalent.
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