Superconductors

Highlights and Recent Results

Phase Diagram of NdFeAsO1-xFx: Essential Role of Chemical Composition

L. Malavasi, G.A. Artioli, M.C. Mozzati, C. Ritter, B. Pahari, B. Maroni, A. Caneschi  J. Am. Chem. Soc. (2010) 132, 2417-2420 [LINK]

In this work, we provided the complete phase diagram of NdFeAsO1-xFx solid solution as a function of electron doping thanks to the careful determination of F- and O-content and phase content. We gave direct evidence of the source of F-depletion in the superconducting main phase, that is, the formation of oxyfluoride spurious phase. The approach reported in this work clearly showed that to give reliable results on these complex new superconducting materials, a rigorous control of the chemical composition of the considered phases has to be carried out.

The figure shows the correlation between the nominal F-doping (i.e., the stoichiometry of F used in the samples synthesis) against the F-content determined by means of EMPA. As can be appreciated, along with the increase in the F-content, the discrepancy between the nominal and effective F concentration increases.

Trend of the transition temperature from the tetragonal to the orthorhombic symmetry (TS, full circles with gray pattern indicating the uncertainty) and of the critical temperature (TC, full stars) against the electron doping of the samples. M above the stars in the phase diagram marks those samples that show long-range magnetic ordering at 2 K.