Structural behavior of Pb$_y$Bi$_{1.95-y}$Sr$_{1.49}$La$_{0.4}$Cu$_{1.15}$O$_{6+\delta}$ for 0<y<0.53

TL;DR

This study investigates how lead substitution affects the phase separation and superstructure in a Bi-based cuprate superconductor using microscopy and diffraction techniques.

Contribution

It provides detailed insights into the development of phase separation and superstructure changes due to lead substitution in Bi cuprates.

Findings

Lead substitution induces phase separation into { extalpha} and {eta} phases.

Superstructure behavior is significantly altered by lead content.

Thermodynamic analysis explains the inevitability of phase mixture.

Abstract

In the Bi cuprates, the presence of a near 1$\times$5 superstructure is well known. Usually, this superstructure is suppressed by the substitution of lead, but there have been reports of a phase separation in so called {\alpha} and {\beta} phases. This paper shows in high detail time how and why the phase separation develops and what happens to the quasi-1$\times$5 superstructure upon lead substitution. For this purpose, the lanthanum- and lead-substituted single-layered superconductor Bi$_{2+z}$Sr$_{2-z}$CuO$_{6+\delta}$ has been investigated by scanning tunneling microscopy and low-energy electron diffraction. The La content was kept constant at slightly under-doped concentration while the Pb content was changed systematically. Thermodynamic considerations show that a phase mixture of {\alpha} and {\beta} phases is inevitable.