WDX-Analysis of the New Superconductors RO(1-x)F(x)FeAs and Its Consequences on the Electronic Phase Diagram

TL;DR

This study uses wavelength-dispersive X-ray spectroscopy to accurately measure fluorine content in RO(1-x)F(x)FeAs superconductors, revealing discrepancies from initial compositions and refining their electronic phase diagrams.

Contribution

It provides the first detailed fluorine content measurements in these superconductors, improving the accuracy of their electronic phase diagrams.

Findings

Fluorine content often deviates from initial weight estimates.

Measured fluorine levels are lower than expected, especially in Sm-based compounds.

Refined phase diagrams better reflect actual sample compositions.

Abstract

Polycrystalline samples of RO1-xFxFeAs (0 < x < 0.25) (R = La, Sm, Gd) were investigated by wavelength-dispersive X-ray spectroscopy (WDX) in the electron microscope to determine the composition of the samples, in particular the fluorine content. It was found that the measured fluorine content can deviate considerably from the initial weight. In the lanthanum compound LaO1-xFxFeAs, we found good agreement mainly for x > 0.05, but for x < 0.05 the fluorine hardly goes into the sample. For the samarium compound we measured less than half the fluorine in the sample as initially weighed at all fluorine concentrations. These measured values are taken into account when drawing the electronic phase diagrams of LaO1-xFxFeAs and SmO1-xFxFeAs. This leads to a more consistent picture of both of the diagrams in comparison to the plot of the initial weight.