Phaseseparation in overdoped Y_{1-0.8}Ca_{0-0.2}Ba_2Cu_3O_{6.96-6.98}

TL;DR

This study investigates phase separation in overdoped YCaBaCuO superconductors using X-ray absorption spectroscopy, revealing a percolation threshold and charge carrier trapping at Ca sites, indicating phase segregation.

Contribution

It provides direct evidence of phase segregation and charge trapping mechanisms in overdoped cuprates through structural measurements.

Findings

Percolation threshold at 12% Ca doping.

Charge carriers are trapped at Ca sites.

Evidence of phase segregation in overdoped samples.

Abstract

The dimpling in the CuO_2 planes of overdoped Y_{1-y}Ca_yBa_2Cu_3 O_{6.96-6.98} (y=0.02-0.2) has been measured by x-ray absorption-fine- structure spectroscopy (Y-K EXAFS). A step-like decrease around 12% Ca indicates a percolation threshold for distorted sites of 5 cells, and thus phase segregation. We conclude the charge carriers added by substitution of Y{3+} by Ca{2+} to be trapped at the Ca sites and their nn environment.